lukewarm.

Etymology tree Middle English leuk Proto-Germanic *warmaz Proto-West Germanic *warm Old English wearm Middle English warm Middle English leukwarm English lukewarm From Middle English leukwarm, lukewarm (“lukewarm, tepid”), equivalent to luke (“lukewarm”) + warm. Compare Saterland Frisian luukwoarm (“lukewarm”), German Low German luukwarm (“lukewarm”); first element is related to Dutch leuk (“lukewarm”), as in leukwater (“lukewarm water”). Compare also West Frisian lijwarm (“lukewarm”), Afrikaans louwarm (“lukewarm”), German Low German lowarm, luwarm (“lukewarm”), German lauwarm (“lukewarm”). First element believed to be an alteration of Middle English lew (“tepid”) (> English dialectal lew), from Old English *hlēowe (“warm, sunny”), from Proto-Germanic *hliwjaz, *hlēwaz, *hlūmaz, *hleumaz (“warm”), from Proto-Indo-European *ḱal(w)e-, *ḱel(w)e-, *k(')lēw- (“warm, hot”). Cognate with Dutch lauw (“tepid”), German lau (“lukewarm”), Faroese lýggjur (“warm”), Swedish ljum (“lukewarm”), ljummen (“lukewarm”) and ly (“warm”), Danish lummer (“muggy”), Danish and Norwegian lunken (“tepid”), dialectal Swedish ljummen (“lukewarm”).