"un" versus "uno"

Question

Is there a general rule for when to use "uno" versus "un"? I know to say "Tengo un minuto" or "Trienta y un minutos" but when I count I say "Trienta y uno".

Answer 1

• un = a/an when used before a singular masculine noun.
• una = a/an when used before a singular feminine noun.
• unos/unas = some or a few when used before plural nouns, masculine or feminine.
• uno = one.

Answer 2

They like to drop the "o" on certain masculine adjectives, "uno", being one of them. "Uno", then, is just the noun meaning 1. Uno, dropping the o, is the adjective and masculine equivalent to "una". Other examples are "primero," "tercero," & "bueno." As they are, those are nouns... 1st, 3rd, and good, but when used as masculine adjetives, they become "primer" (el primer año), "tercer" (el tercer perro), and "buen" (buen día). This pattern also explains why "algún" and "cualquier" do not end in "o", when their fememine versions "alguna" and "cualquiera" end in their normal "a". There is no noun forms of those words, so they are always algún & cualquier unless it's plural (algunos).

This is to my understanding.

Answer 3

I'm not positive on this but I think that it's mostly a stylistic difference or possibly for emphasis. I know that if you are saying it's * a * item then it is "un/a".

Someone please correct me if I'm wrong.