That's medieval rhyming slang for ya, which also gave us Dick from Richard via Rick. This is also the root of "penis" as a definition for "dick", with the use of "dick" as a metonym for "man" and subsequently "man" as an implied metonym for "penis", via the placeholder phrase "Tom, Dick, and Harry" meaning "unspecified people".

I wrote this comment in the spirit of linguistic descriptivism (discussing past use of language) rather than prescriptivisism (commanding the reader to use language in a certain way going forward), in order to not carry water for gender essentialism, transphobia, or sexism, due to the direct association of penises with manhood present in the etymologies that I mentioned.