means Full of fun and high spirits; inclined to joke, frolic, or treat things lightly rather than in earnest.

from Built from "play" plus the suffix "-ful," meaning "full of play." "Play" descends from Old English "plega" (game, sport, frolic) and the verb "plegan," with cousins in Old Saxon and Dutch; its deeper roots are murky, possibly tied to a sense of brisk movement or exercise. The "-ful" ending is the same one in "joyful" and "hopeful" — once literally "full," now just a tidy way of saying "having plenty of."