(sup) v.t. & v.i. supped, sup·ping
To take (fluid food) in successive mouthfuls, a little at a time; sip.
—noun A mouthful or taste of liquid or semiliquid food. [OE sūpan drink]

(sup) v. supped, sup·ping v.i.
To eat supper.
—v.t. Obs. To furnish with or invite to supper. [<OF soper, super; ult. origin unknown]

Assimilated var. of SUB–.