glib

Glib is likely a shortened form of the obsolete English word glibbery, meaning "slippery," which itself came from Low German or Dutch glibberig, also "slippery." Separately, it has also been traced to a borrowing from Irish glib.

The word seems to have moved from describing something physically slippery to describing speech that slides too easily, fluent but lacking weight or sincerity.

It's worth comparing dialectal English lib and Old English lib, meaning "to castrate," along with related Low German and Old Dutch lubben — though the exact connection to glib isn't spelled out beyond the resemblance.