Good and Bad

adjective	apocope		meaning
bueno	buen		good
malo	mal		bad

Bueno and malo can either precede masculine nouns (in their shortened form) or follow the noun (in their original form); the latter gives them a slight emphasis.

Por ejemplo…

Pablo es un buen hombre.		Pablo is a good man.
Pablo es un hombre bueno.		Pablo is a (truly) good man.

Numbers

Four numbers have apocopes.

adjective	apocope		meaning
primero	primer		first
tercero	tercer		third
uno	un		one, a
ciento	cien		a hundred

The first three must be used when they precede a masculine singular noun.

Por ejemplo…

Este es mi primer coche.		This is my first car.
Tengo un hermano.		I have one brother.

When the number does not precede a noun but rather stands alone as a pronoun, it maintains its original form:

Este es el primero.		This is the first one.
Sí, tengo uno.		Yes, I have one.

The above adjectives are not shortened when used with feminine or plural nouns.

una hermana		one woman
los primeros coches		the first cars

Ciento is a special case: it shortens to cien when it precedes a plural noun or when it multiplies the number that follows.

cien euros		100 euros
cien mil		100,000

But not when it’s part of a larger number.

ciento cuarenta		140
dos cientos		200

Indefinite Adjectives

adjective	apocope		meaning
alguno	algún		some
ninguno	ningún		no, none

These follow the exact same rules as primer and tercer.

Por ejemplo…

¿Hay algún baño aquí?		Is there a bathroom here?
No hay ningún problema.		There’s no problem.