El asistente (assistant) La asistenta (assistant)
El infante (child under 7; La infanta (child; Span. Royal
also Span., Royal Prince) 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.

N.B.—

Un abogado makes in the fem. Una muger abogado
Un médico " " " " " médico
Un comadrón " " " " comadre (midwife)

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 muger (woman)
El macho cabrío or cabrón (he-goat) La cabra (she-goat)
El marido (husband) La muger (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)