Green’s Dictionary of Slang

a crushing blow; also fig.

1854		‘Cuthbert Bede’ Adventures of Mr Verdant Green (1982) II 166: There’s a squelcher in the bread-basket, that’ll stop your dancing, my kivey!
1876		Besant & Rice Golden Butterfly II 82: In that position he used to write his leading articles. Squelchers, some of them; made gentlemen of opposite politics cry.
1890		‘Doss Chiderdoss’ ‘Unexpected Places’ Sporting Times 8 Mar. 1/3: Next I saw him as a welsher, which I thought a final squelcher.
1938		H.M. Anderson Strip Tease 38: [of a verbal repartee] A frequent reply to this squelcher [...] is the flatulent bird or ‘Bronx cheer’.
1986		D. Barker (con. c.1945) Life in Jazz 196: I generally quieted these big mouths with this squelcher, ‘Bix was misunderstood’ [etc].