Crossword clue: one of several species of swallows, usually having the tail less deeply forked than the tail of the common swallows.
1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).
Possible answers
any of various swallows with squarish or slightly forked tail and long pointed wings; migrate around Martinmas