late 14c., "unaccented syllable or note," from L. thesis
"unaccented syllable in poetry," later "stressed part of a metrical foot," from Gk. thesis
"a proposition," also "downbeat" (in music), originally "a setting down or placing," from root of tithenai
"to place, put, set," from PIE base *dhe-
"to put, to do" (see factitious
). Sense in logic of "a proposition, statement to be proved" is first recorded 1570s; that of "dissertation written by a candidate for a university degree" is from 1650s.