(especially of a liquid) only slightly warm. (Cambridge Dictionary)
Moderately warm: Tepid. (Merriam – Webster)
Lacking conviction: Half – hearted. (Merriam – Webster)
Something, especially a liquid, that is lukewarm is only slightly warm. (Collins Dictionary)
If you describe a person or their attitude as lukewarm, you mean that they are not showing much enthusiasm or interest. (Collins Dictionary)
(of liquid or food that should be hot) only moderately warm; tepid. (Oxford Dictionaries)
Showing little enthusiasm. (Oxford Dictionaries)
On being lukewarm.
What does Jesus mean: “I wish you were cold or hot, not lukewarm”?