As nearly always with learning grammar there are exceptions to the general rules. With nouns in Spanish try to remember the following changes:
Nouns that end in –o that are feminine:
There are words that appear to be masculine from their -o ending but they are feminine.
Often these words have been shortened:
la radio [is orginially from “la radiografía”] (radio)
la foto [la fotografía] (photograph)
la moto [la motocicleta] (motorbike)
The nouns below appear to be masculine but they are feminine:
la modelo (model)
la mano (hand)
Therefore, when using adjectives with these nouns you must remember to make them feminine too:
Un coche de segunda mano (a second-hand car)
No es una buena foto. (It isn’t a good photo)
Nouns that end in –a but are masculine:
There is a group of nouns that end in –ma which are masculine:
el clima (climate/weather)
el pyjama (pyjamas)
el problema (problem)
el sistema (system)
el tema (theme/topic)
Other words that end in –a but are masculine include the following:
el mapa
el planeta
el día
Nouns describing a male person:
el atleta (athlete)
el guía (guide)
el policía (policeman)
Nouns ending in “–ista” are normally masculine unless referring to a female:
el periodista (male journalist) – la periodista (female journalist)
el turista (male tourist) – la turista (female tourist)
el dentista (male dentist) – la dentista (female dentist)
el futbolista (footballer) – la futbolista (female footballer)
Particularly interesting is where certain words can be masculine or feminine, but they change meaning:
el capital (capital/money) > la capital (capital city)
el orden (order/tidiness) > la orden (order/command)
el disco (disc/record) > la disco (the disco)
el manzanilla (type of fortified wine) > la manzanilla (camomile tea)
el cometa (comet) > la cometa (kite)
Some nouns have recently introduced a feminine form whereas before they only had a masculine form:
la jefa (boss) [from el jefe]
la dependienta (shop assistant) [from el dependiente]
la presidenta (president) [ from el presidente]
la estudianta (student) [from el estudiante]