jolly (adj.) Look up jolly at Dictionary.com
c.1300 (late 13c. as a surname), from Old French jolif "festive, merry, amorous, pretty" (12c.) of uncertain origin (cognate with Italian giulivo "merry, pleasant").

Perhaps a Germanic loan-word from a source akin to Old Norse jol "a winter feast" (see yule), or from Latin gaudere "to rejoice," from PIE *gau- "to rejoice" (see joy). For loss of -f, compare tardy, hasty. Related: Jollily; jolliness.