expression
sparing no effort; taking pains to do
A set phrase meaning to do something without begrudging the effort, often used in formal or written contexts to describe diligent, painstaking work.
彼は労を惜しまず、毎日遅くまで研究を続けた。
He spared no effort and continued his research late every day.
労を惜しまずに準備したおかげで、発表は大成功だった。
Thanks to the painstaking preparation, the presentation was a great success.
A set phrase combining 労 (effort, labor) with the negative continuative form of 惜しむ (to begrudge, to spare), literally 'without begrudging effort'.