The adverb 'wantonly' is built directly upon its adjectival base, 'wanton'. The story of 'wanton' begins in Old English as wantowen, a compound describing something or someone 'lacking discipline' or 'untrained'. Its first element, wan-, is a common Germanic prefix denoting absence or deficiency, akin to the 'wan-' in 'wane'. The second element derives from the past participle of the verb tēon, meaning to draw or pull, which by extension came to signify being drawn into line, i.e., educated or disciplined. Thus, the literal sense was 'lacking in training or moral restraint'. Over centuries, this core idea of unbridled behavior branched into the modern meanings of being cruelly reckless or sexually promiscuous. The suffix '-ly', of ancient Germanic lineage, is then applied to form the adverb, describing an action performed in such an undisciplined or unrestrained manner.

Structure: wanton (adjective) + ly (adverb suffix) - wanton: From Middle English wantowen, meaning undisciplined, from Old English wan- (lacking) + togen (trained, past participle of tēon to draw, pull, educate). The Old English prefix wan- is of Germanic origin, meaning 'deficient, lacking'. The root togen relates to discipline or cultivation. - ly: A suffix of Germanic origin (Old English -līce) used to form adverbs from adjectives, indicating manner or quality.