i-adjective
Describes liquids or objects that are not hot enough, often with a negative nuance of being disappointingly cool.
スープがぬるくなってしまった。
The soup has gone lukewarm.
ぬるいお茶はおいしくない。
Lukewarm tea doesn't taste good.
i-adjective
Used for attitudes, policies, or judgments that are too easygoing or not strict enough. Often carries a critical tone.
See also: 緩い (ゆるい)
彼の指導はぬるいと言われている。
His coaching is said to be too lenient.
そんなぬるいやり方では成功しない。
You won't succeed with such a lax approach.