Fetching details from the dictionary...
to work hard at; to devote oneself to; to be diligent in
彼女は研究に十年勤しんだ。
She devoted herself to research for ten years.
農夫は畑仕事に一日中勤しんでいる。
The farmer is diligently working in the fields all day.
彼は毎日、自分の技芸を磨くべく勤しむのだ。
He works hard every day to refine his craft.