"assembly of freemen," mid-12c., from Old English gemot "meeting" (especially of freemen, to discuss community affairs or mete justice), "society, assembly, council," from Proto-Germanic *ga-motan (compare Old Low Frankish muot "encounter," Middle Dutch moet, Middle High German muoz), from collective prefix *ga- + *motan (see meet (v.)).
"debatable; not worth considering" from moot case, earlier simply moot (n.) "discussion of a hypothetical law case" (1530s), in law student jargon. The reference is to students gathering to test their skills in mock cases.
"to debate," Old English motian "to meet, talk, discuss," from mot (see moot (n.)). Related: Mooted; mooting.