Know why cattywampus was trending last week?
Old English full "completely, full, perfect, entire, utter," from Proto-Germanic *fullaz (cf. Old Saxon full, Old Frisian ful, Old Norse fullr, Old High German fol, German voll, Gothic fulls), from PIE *pele- (1) "to fill" (see poly-).
Adverbial sense was common in Middle English (full well, full many, etc.). Related: Fuller; fullest. Full moon was Old English fulles monan; first record of full-blood in relation to racial purity is from 1812. Full house is 1710 in the theatrical sense, 1887 in the poker sense.
"to tread or beat cloth to cleanse or thicken it," late 14c., from Old French fouler, from Latin fullo (see foil (v.)); Old English had the agent-noun fullere, probably directly from Latin fullo.