I found this quite fascinating. This word is the final remnant in Modern English of the wan- prefix, once prevalent in Old English, barely making it into Middle English, other than Scotland and the North, and leaving this sole example in the present. First the etymology of wanton, then the info on the prefix, all taken from OED.
wanton, adj. and n.
Middle English wantowen , < wan- prefix + towen < Old English togen past participle of téon tee v.1 to discipline, train. The word thus literally means ‘undisciplined’; compare untowe(n adj., and the equivalent German ungezogen; also Middle English welitowen well-brought-up. Middle English wantowen , < wan- prefix + towen < Old English togen past participle of téon tee v.1 to discipline, train. The word thus literally means ‘undisciplined’; compare untowe(n adj., and the equivalent German ungezogen; also Middle English welitowen well-brought-up.
a prefix expressing privation or negation (approximately equivalent to un- prefix1 or mis- prefix1), repr. Old English wan-, wǫn-, corresponding to Old Frisian. wan-, won-, Old Saxon wan- (only in wanskefti misfortune = Old English wansceaft), Middle Low German, Middle Dutch wan- (modern Dutch in many new formations, esp. in the sense ‘wrong’, ‘mis-’, as in wanbestuur misgovernment, wanluid discordant sound), Old High German wan-, wana (only in wanwâfan unarmed, wanaheil unhealthy, infirm, wanawizzi lacking wit, insane), Middle High German wan- (only in wanwitze inherited from Old High German), modern German wahn- (in wahnwitz, wahnsinn insanity, commonly apprehended as compounds of wahn n., delusion; also in some dialect words, chiefly adopted from Low German); ON., Swedish, Danish van- (in many old formations, to which modern Swedish and Danish have added many more, chiefly adopted from Low German). The prefix is in origin identical with wane adj.
In Old English the number of words formed with the prefix is considerable, but none of them has survived into modern English, and only one (wanspéd, ill-success) into Middle English Of the many new formations that arose in Middle English, only wantoȝen, undisciplined, wanton adj. and n., still survives in use (with no consciousness of its etymological meaning); wanhope and wantrust may have been suggested by the equivalent Middle Dutch forms. It was in the north that the prefix was most prolific, and it probably continued to be productive far into the modern period. The following words, peculiar to the Scottish and northern dialects, are recorded in the Eng. Dial. Dict., mostly with examples (or references to glossaries etc.) from the 18th c., but few if any of them are now in current use:— wancanny adj., wanchancy adj., wancheer grief, sadness, wancouth adj. = uncouth, wandeidy adj., mischievous, wandought n. and adj., wanearthly adj., wanease n., wanfortune n., wanfortunate, adj. wanhap n., wanliesum adj., wanlit adj., wanluck, wanown’t adj. = unowned, wanreck ‘mischance, ruin’, wanrest n., wan-thriven adj., wanuse misuse, waste, wanweird n., wanworth adj. and n.
Dave, I see the un- prefix for negation also existed in Old English. Is there any indication that the two prefixes are connected. I can’t see anything in OED to suggest this but they are so similar in sound (if I’m reading that phonetic symbol correctly) that one could be forgiven for thinking them cognates.