a person who is unknown or with whom one is unacquainted
She was a stranger to me
a person unfamiliar in the place in question; a foreigner or alien
(+ to) a person who is ignorant of or unacquainted with something
a stranger to books
in Britain, a person who is not a member or official of the House of Commons
the Strangers’ Gallery
[Middle English via Old French estrangier foreign, foreigner, from Latin extraneus: see strange]