1. Words of Greek etymology ending in ma:

El dilema - the dilemma
El diploma - the diploma
El epigrama - the epigram
El problema - the problem
El síntoma - the symptom
El telegrama - the telegram
etc., etc.

But

La amalgama - the amalgamation
La diadema - the diadem
La estratagema - the stratagem
La proclama - the proclamation

2. Most of the compound nouns (very few in number):

El cortaplumas - the penknife
El guardacosta - the coasting-vessel
El paraguas - the umbrella
El tirabala - the popgun

3. El día (the day):

El Etna - (Etna (volcano))
El mapa - the map
El sofá - the sofa
El Volga [1] - the Volga
And all words ending in accented a.

4. Masculine nouns ending in d:

El adalid - the warrior or chieftain
El ardid - the trick
El ataúd - coffin
El césped - the turf, lawn
El sud - the south

5. Masculine nouns ending in ión:

El embrión - the embryo
El gorrión - the sparrow
El morrión - parts of an armour
El sarampión - measles

6. Feminine nouns ending in i or y:

La diócesi - the diocese
La grey - the flock
La ley - the law
La metrópoli - the metropolis
Almost all.

7. Feminine noun ending in j:

La troj - the granary

8. Feminine nouns ending in l:

La cal - lime
La capital - capital--town
La cárcel - prison
La col - cabbage
La miel - honey
La piel - skin
La sal - salt
La señal - signal
La vocal - vowel
And a few more.

9. Feminine nouns ending in n:

La cargazón - the load
La crin - the horsehair
La desazón - the ailment
La imagen - the image
La razón - the reason
La sinrazón - the injustice
La sartén - the frying-pan
La sien - the temple
Almost all.

10. Feminine nouns ending in o:

La mano - the hand

Only word, excepting "nao" (ship), now obsolete, and "seo" (cathedral), little used.

11. Feminine nouns ending in r:

La flor - the flower
La labor - the needlework
La segur - the axe
Almost all.

12. Feminine nouns ending in s:

La bilis - the bile
La crisis - the crisis
La elipsis - ellipsis
La lis - fleur-de-lis
La mies - the crop
La perífrasis - the periphrase
La tos - the cough
And a few others.

13. Feminine noun ending in u:

La tribu - the tribe

14. Feminine nouns ending in z:

La codorniz - the partridge
La cerviz - the cervix
La cruz - the cross
La coz - the back-kick
La luz - the light
La nariz - the nose
La nuez - the nut
La pez - the pitch
La voz - the voice
La raíz - the root
La tez - the complexion
La vez - the time, once, etc., etc.
And a few others less important.

15. Feminine nouns ending in e. (This is the most numerous list of exceptions):

Las aves - the birds
La barbarie - the barbarity
La base - the basis
La calle - the street
La carne - the flesh
La fiebre - the fever
La fuente - the fountain
El hambre (f.), - the hunger
La mente - the mind
La noche - the night
La parte - the part
La quiete - the quiet
La sangre - the blood
La serpiente - the serpent
La torre - the tower

Besides the masculine and feminine genders, some nouns are called: de género común, epiceno, and ambiguo. The noun is called "de género común" (common gender) when with the same termination it may indicate both a male and female being by using a different article:

Un--una albacea - an executor, executrix
Un--una artista - an artist, artiste
Un--una Belga[2] - a Belgian
Un--una idiota - an idiot
Un--una indígena - a native
Un--una mártir - a martyr
Un--una reo - a culprit
Un--una culpable - a culprit
Un--una gimnasta - a gymnast
Un--una homicida - a murderer, a murderess
Un--una suicida - one who commits suicide
Un--una testigo - a witness

The noun is called Epicene when, with the same termination and the same article, it indicates both male and female:

El águila - the eagle--male and female
El buitre - the vulture--male and female
El avestruz - the ostrich--male and female
La rata - the rat--male and female

Distinction would be made by adding "macho" or "hembra."

El águila macho - the eagle--male
El avestruz hembra - the ostrich--female

The term "ambiguo" is applied to nouns which are masculine or feminine, with different meaning, or the gender of which is not well defined:

,

El aroma - the aroma	La aroma - the acacia flower
La or el arte - the art	Los or Las artes - the arts, generally _fem_.
Las bellas artes - the fine arts, always _fem_.
La barba - the beard	El barba - a character in Spanish plays
El cabecilla - chieftain or ringleader of rebels	La cabecilla - the little head
El calavera - the madcap	La calavera - the skull
El canal - the canal	La canal - the gutter
El capital - money	La capital - the town
El cólera - cholera	La cólera - wrath
El cometa - comet	La cometa - the kite, _toy_
El corte - the cut	La corte - the court
El cura - the priest	La cura - the cure
El doblez - the fold	La doblez - duplicity
El or la dote - dowry, generally _fem_. in the _pl_. always _fem_.	Las dotes - good parts, gifts
El fantasma - the phantom	La fantasma - the bogie-man
El frente - the front	La frente - the forehead
El haz - the sheaf	La haz - face, surface
Lente - lenses, doubtful gender
La orden - command, order for goods, etc.	El orden (order); as, buen orden - good order
Las sagradas órdenes - holy orders	Las varias órdenes - various religious orders
El parte - report	La parte - part
El pendiente - ear-ring	La pendiente - slope
El pez - fish	La pez - pitch
El tema - exercise, theme	La tema - fear, obstinacy
Tilde - ~, doubtful gender

"Mar" (sea) is either Masc. or fem., but names of particular seas are all masculine:

El mar rojo - the Red Sea
El mar Caspio - the Caspian Sea

The compounds of "mar" are feminine:

Baja mar - low sea
Pleamar - high water

The following masculine nouns have their equivalent feminine formed by inflexion:

El abad - abbot	La abadesa - abbess
El actor - actor	La actriz - actress
El barón - baron	La baronesa - baroness
El canónigo - canon	La canonesa - canoness
El cantor - singer	La cantatriz - singer
El conde - count	La condesa - countess
El diacono - deacon	La diaconisa - deaconess
El duque - duke	La duquesa - duchess
El elector - elector	La electriz - electress
El emperador - emperor	La emperatriz - empress
El filósofo - philosopher	La filosofesa - philosopher
El gallo - cock	La gallina - hen
El héroe - hero	La heroína - heroine
El poeta - poet	La poetisa - poetess
El principe - prince	La princesa - princess
El profeta - prophet	La profetisa - prophetess
El rey - king	La reina - queen
El sacerdote - priest	La sacerdotisa - priestess
El vizconde - viscount	La vizcondesa - viscountess
El Zar - czar	La Zarina - czarina

Notice also:

El asistente - assistant	La asistenta - assistant
El infante - child under 7; also Span., Royal Prince	La infanta - child; Span. Royal Princess
El pariente - relative	La parienta - relative
El presidente - president	La presidenta - president
El sirviente - manservant	La sirvienta - maidservant

There are only a few more of this class.

The following nouns of persons and animals have two different forms to represent the two sexes:

El buey - ox	La vaca - cow
El caballo - stallion	La yegua - mare
El carnero - ram	La oveja - ewe
El fraile - friar	La soror - sister
El hombre - man	La mujer - woman
El macho cabrío or cabrón - he-goat	La cabra - she-goat
El marido - husband	La mujer - the wife
El padre - father	La madre - mother
El padrastro - step-father	La madrastra - step-mother
El padrino - god-father	La madrina - god-mother
El toro - bull	La vaca - cow
El yerno - son-in-law	La nuera - daughter-in-law

Many names of animals are either common, as:

El ánade, la ánade - the duck
El liebre, la liebre - the hare
El tigre, la tigre - the tiger, tigress

Or they change o of the masculine into a or add a, to form the feminine, as:

Un ganso - a gander	Una gansa - a goose
Un león - the lion	Una leona - a lioness
Un mulo - a mule	Una mula - a she-mule
Un pollino - an ass	Una pollina - a she-ass

Most are epicene as already stated (p. 246).