You can picture a horse with no bridle on it. The old meaning of wanton is simply not trained, not held. Nothing is pulling it back, so it goes wherever it goes. Sometimes that is harmless running about; sometimes it tramples the garden. Almost every later use of the word can be read as that one picture pointed in a different direction.
可以想成一匹沒有套上韁繩的馬。wanton 最早的意思就是「沒被教過、沒被管住」。沒有東西拉住牠，所以牠想往哪裡跑就往哪裡跑。這份自由有時候是無害的亂跑，有時候是把花圃整個踩爛。後來這個字的每一個用法，幾乎都可以看成同一個「沒人拉住」的畫面，只是朝不同方向長出去。
From the word’s history
Middle English wantoun is wan- (not, un-) plus towen, the old past participle of teon (to train, to lead, to discipline). So the word literally says un-trained, un-led.
中古英語 wantoun 由 wan-（不、沒有）加上 towen 組成；towen 是古英語 tēon（訓練、牽引、管教）的過去分詞。字面上就是「沒被管教過、沒被牽住」。今天的每個用法，都還看得到這個字根。
Wiktionary, "wanton"
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