Green’s Dictionary of Slang

1. to take the entire length of the penis into one’s mouth, and thus down one’s throat, during fellatio.

1979		in Playboy Aug. 52: She proceeded to deep-throat me.
1991		C. Hiaasen Native Tongue 39: Students [...] were instead exposed to a mattress-level montage of Latin porn star Pina Kolada deepthroating a semi-pro soccer team.
1999		‘Master Pimp’ Pimp’s Rap 54: As she slowly deep throated my rod, her sexy eyes told me I was going to love every minute of it.
2004		N. Kelley ‘The Code’ in Brooklyn Noir 191: Knee-deep into deep-throating Dominique, Code could feel his own backdoor being prepared for a rear-entry maneuver.
2005		L. Theroux Call of the Weird (2006) 61: I’m not into rough sex. I don’t mind you deepthroating me but treat me right.
2019		D. Winslow Border [ebook] He presses her head down. ‘Deep throat me’.

2. in a non-sexual or semi-sexual sense, e.g. to suck suggestively on a straw.

1999

‘Master Pimp’ Pimp’s Rap 48: She crossed her big pretty legs and enticed me by deep throating the straw in her drink giving me the impression that she knew how to use her mouth for more than just to talk.