Anything that can be hot or cold can be lukewarm. But “luke” doesn’t exist on any other continuum—there’s no lukedim or lukefirm or lukeajar. That’s because “luke” comes from Old English hlēo which means “the lee side of a boat” which itself came from Latin calēre, “to be warm.” Lukewarm is redundant. It means warm-warm.
@Cdespinosa aw, you mean my sibling and i aren't allowed to say lukecold (mildly cold) anymore?