For a relatively obscure word, "hooker" has far too many meanings. Maybe we should deprecate some of them.

My God! I just learned this word myself! I'm in a psychology Master's program, and my Stats professor is a wonderful old fellow, 80 years' worth of sarcasm and sophistry, and a WWII veteran. He used the phrase "a hooker of gin" to mean what I would call "a slug of gin" (or similar). Since my background's in linguistics, I had to ask him about it, but he was surprised to hear I didn't know it.

As far as I can recall, this is not a current usage, but an archaism. I've never heard anyone other than Dr. Hunter say it.