According to Today I Found Out, the association between dick and man may be the reason dick eventually came to mean penis, although this didn’t happen until centuries later. The first recorded use of dick meaning penis was from the 1890s, and it was British Army slang. However, that meaning had probably already been in use for a few decades.
The use of dick to mean jerk, or generally a nasty person, also probably dates to the 19th century. This may be the usage Jane Austen (above) had in mind in her 1817 book “Persuasion,” when she wrote, “He had, in fact, though his sisters were now doing all they could for him, by calling him ‘Poor Richard,’ been nothing better than thick-headed, unfeeling, unprofitable Dick Musgrove, who had never done any thing to entitle himself to more than the abbreviation of his name” (via Grammarphobia).
“Dick” has had other meanings over time, including meaning a declaration, a type of hard cheese, an apron, a dictionary, a detective, a whip, and nothing at all (as in “I have dick to say”), according to Today I Found Out.
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