expression, adverb
without a trace; completely gone
Used when something disappears entirely, leaving no physical or visible evidence behind. Often used with verbs like 消える, なくなる, or 去る.
犯人は跡形もなく消え去った。
The culprit vanished without a trace.
雪は朝には跡形もなく溶けていた。
The snow had melted away completely by morning.
跡形 is the noun meaning 'trace' or 'vestige'; 跡形もなく is the adverbial phrase meaning 'without a trace'.
From 跡形 (trace, vestige) + も (even) + なく (adverbial form of ない, not exist). Literally 'even a trace not existing'.