taru-adjective, adverb taking the 'to' particle
diligent; absorbed; engrossed
Literary or formal word describing someone who is diligently absorbed in a task, often with a sense of single-minded devotion. Commonly used as 〜とした or 〜と.
彼は汲々として研究に打ち込んでいる。
He is diligently absorbed in his research.
汲々と働く姿は周囲の尊敬を集めた。
His figure, working diligently, earned the respect of those around him.
The exact derivation is uncertain. The kanji 汲 means 'draw water', and the reduplicated form 汲々 likely developed the sense of continuously drawing or applying oneself, hence 'diligent'.