Sometimes words that are ostensibly given as translations of another aren't one-to-one correct. For example, de and por are often given to mean lots of different English words, none of which captures the full meaning of the Spanish equivalent.
I hear amigo used more often among Spanish-speaking folk (I live in California, if that's relevant) than in English. For example, when visiting a taqueria, the cook will often greet me with, "Welcome, mi amigo", even if I've never met him before.
While it's not unheard of for English-speakers to greet strangers with, "Welcome, friend" — particularly in some regions in America — it seems significantly less common; for some (like me) it comes off with a touch of presumptuousness — that to use that word there should be previous acquaintanceship. (For whatever reason, I adopt an entirely different — and welcoming — attitude when the phrase is spoken in Spanish)
Perhaps it's regional and cultural, but I was wondering if there is an actual difference definitionally between friend and amigo in a way similar to de and por — any nuance at all.