10 letters · 15 points in Scrabble
noun a quantity that does not vary
adjective not liable to or capable of change
originEtymology tree Proto-Indo-European *né Proto-Indo-European *n̥- Proto-Italic *n̥- Latin in-bor. Middle English in- English in- English variable English invariable From in- + variable.
Etymology from Wiktionary, CC BY-SA 3.0