godan verb (-su), transitive verb
wave back
Used in the phrase 手を振り返す, meaning to wave one's hand in return to someone who waved first.
友達が手を振ったので、私も手を振り返した。
My friend waved, so I waved back.
Standard kanji spelling.
Kana spelling is common in everyday writing.
振る is a general verb for waving or shaking something, while 振り返す specifically means waving back in response.
Compound of 振り (from 振る, 'to wave') + 返す ('to return').