OED gives at the very least two diverse senses for this phrase. That of feminine genitalia is attested as early as 1699, but it's actually not viewed as with the perception this means "coward". One other one, which I copy below, will be the purported source of pussy g., “.onion” https://johnnyfowfl.ziblogs.com/29932801/terror-us-no-further-a-mystery