hobnob: [18] In Shakespeare’s Twelfth Night, Sir Toby Belch says ‘Hob, nob, is his word: give’t or take’t’; from which it has been deduced that the hob of hobnob represents have and that the nob represents the now obsolete nave ‘not have’ (formed in the Old English period by adding the negative particle ne to have). In Middle English these would have been habbe and nabbe.
When hobnob first appears as a verb, in the mid 18th century, it means ‘drink together’ – perhaps from the notion of buying alternate rounds of drinks, or drinking toasts to each other in turn. The modern sense ‘associate familiarly, socialize’ is not recorded before the early 19th century. => have[hobnob etymology, hobnob origin, 英语词源]