Green’s Dictionary of Slang

(US) a knife.

1942		N. Algren Never Come Morning (1988) 114: ‘I bought it from a bum.’ ‘Same bum who sold you the spring-blade stabber?’.
1956		‘Hal Ellson’ ‘Cool Cat’ in Tell Them Nothing (1956) 102: ‘Get your stabber out.’ ‘What you want my knife for?’.
1979		Pittsburgh Press (PA) 15 Nov. 21/1: Williams [...] pushed his thin-bladed ‘stabber’ into the mouth of an oyster and slit it open.