habnab (n.)

1763, "to drink to each other," from hob and nob (1756) "to toast each other by turns, to buy alternate rounds of drinks," alteration of hab nab "to have or have not, hit or miss" (c. 1550), which is probably ultimately from Old English habban, nabban "have, not have," (that is, "to take or not take," used later as an invitation to drinking), with the negative particle ne- attached (from PIE root *ne- "not"), as was customary; see have. Modern sense of "socialize" is 1866. Related: Hobnobbed; hobnobbing.