Unfamiliar means not known to you. A face you cannot place, a road you have never driven.
It takes with when the person is the subject and to when the thing is: unfamiliar with the software, unfamiliar to anyone who grew up here. That pair catches learners out regularly and is worth learning together. The word is neutral and carries no criticism, which makes it useful for saying you do not know something without sounding ignorant. Its opposite, familiar, also means over-friendly, which unfamiliar does not mirror at all.
1adjectiveunfamiliarNot known or recognised.
“He woke in an unfamiliar room.”
Proto-Indo-European
*dʰeh₁-
Latin
familiāris — pertaining to servants; pertaining to the household
Middle English
familiar,familier
English
familiar
English, today
unfamiliar
From un- + familiar. familiar comes from Middle English familiar,familier, from Latin familiāris (“pertaining to servants; pertaining to the household”). by surface analysis, family + -ar. familial. Displaced native Old English hīwcūþ.
Etymology from Wiktionary, CC BY-SA