adverb
wholeheartedly; intently; with undivided attention
Describes doing something with complete focus, free from distracting thoughts. Often used with verbs like 取り組む, 打ち込む, or 励む.
See also: 余念なく
彼は余念もなく研究に打ち込んでいる。
He is wholeheartedly absorbed in his research.
子供たちは余念もなく遊んでいる。
The children are playing intently.
From 余念 (distracting thoughts) + も (even) + なく (without). Literally 'without even stray thoughts'.