Where does “luach” come from?

luach (Middle Irish) comes from Old Irish lóg, from Proto-Celtic lowgos, from Proto-Indo-European leh₂w- — to seize, gain; benefit, prize.

Ancestry of “luach”, step by step

Step	Language	Word	Meaning
1	Old Irish	lóg	value, equivalent, worth; reward, requital,...
2	Proto-Celtic	lowgos	—
3	Proto-Indo-European	leh₂w-	to seize, gain; benefit, prize

luach — Etymology, Origin & Word History | Etymology Explorer