Noun Endings

In Spanish every noun has a gender, that is it is identified as being either a feminine or masculine word.  The gender of some words are obvious.  Words that refer to a male, such as father, brother, etc., are masculine.  Those words that refer to a female, such as mother or sister are feminine.  For all other words you have to learn the correct ending. 

Usually you can identify the gender of a noun by looking at the last letter in the word.  For example:

Nouns that end with the letter "o".  These are usually masculine nouns.

el muchacho   boy
el hermano   brother
el gallo   rooster
el museo   museum
el libro   book
     

Note: there are some exceptions:
la mano   hand
la foto   photograph

It is la foto because it the word is an abbreviated form of la fotografía.
     

Nouns that end with the letter "a".  These are usually feminine nouns.
la muchacha   girl
la hermana   sister
la gallina   hen
la montaña   mountain
la escuela   school
     

Note: there are two exceptions:

    
Nouns that end the letter "a" that are masculine usually  derived from greek words:
el día   day
el mapa   map
el programa   program
el clima   climate
el tema   theme
     
Nouns that end with the letters "ista".  These nouns usually refer to a profession or political persuasion and are masculine when refer to a man and feminine when referring to a woman.
el dentista   dentist (male)
la dentista   dentist (female)
el novelista   novelist (male)
la novelista   novelist (female)
     

Other feminine endings:

    
All nouns ending in "dad", "tad", "tud", "umbre", "ción" or "sión" are feminine.
la ciudad   city
la dificultad   difficulty
la actitud   attitude
la muchedumbre   crowd
la nación   nation
la inversión   investment
     

Nouns ending with the letter "e"

    
Most nouns that end in "e" that do not refer to human beings are masculine.
el parque   park
el coche   car
el café   coffee, cafe
el aire   air
el accidente   accident
     
Note: these are common exceptions which are feminine nouns.
la calle   street
la llave   key
la clase   class
la noche   night
la gente   people
la tarde   afternoon
     

Nouns ending with the letters "nte"

    

Nouns that end in with the letters "nte" usually refer to people and can be used for both genders.  Many Spanish speakers change "nte" to "nta" when speaking about a female.
el presidente   president (male)
la presidente   president (female)
la presidenta   president (female)
     
el asistente   assistant (male)
la asistente   assistant (female)
la asistenta   assistant (female)