The word 'wilful' is a direct descendant of Old English wilful, a compound of will (desire, intention) and -ful (full of). The core concept, 'will', originates from the Proto-Germanic weljaną, meaning "to want" or "to wish," which itself can be traced back to the Proto-Indo-European root welh₁-, signifying "to choose" or "to wish." The literal Old English sense of "characterized by strong desire" evolved in two distinct directions in modern English. One branch retained a neutral or positive sense of "intentional" (as in 'wilful act'), while the other developed a strongly negative connotation of being obstinately self-willed and disregarding of others, capturing the notion of being excessively "full of one's own will."

Structure: will + ful - will: From Old English will(a), meaning "desire, intention, determination." It is a Germanic root functioning as the core noun stem. - ful: From Old English -ful, an adjective-forming suffix meaning "full of" or "characterized by."