As they said, "aleatorio", or I usually say "al azar". For example, if I say "agarre una moneda al azar" means "I grabbed a random coin", sounds more natural than saying "agarre una moneda aleatoria", which sounds more like a textbook sentence than an everyday life sentence.

Depends on the context

at random: al azar. -------------------------- The word 'random' is also used for technology purposes. Like, random access memory, which means 'memoria RAM'. We also use 'random' as a synomym for nonsenses... In my country (Argentina) 'random' is commonly used to say 'cualquiera'. It means you are saying nonsenses. Check this link. http://www.wordreference.com/es/translation.asp?tranword=random

Aleatorio``````````````````````

aleatorio