英语词源字典 - 在线词源网站

simplicity (n.)[simplicity 词源字典]: late 14c., "singleness of nature, unity, indivisibility; immutability," from Old French simplicite (12c., Modern French simplicité), from Latin simplicitatem (nominative simplicitas) "state of being simple, frankness, openness, artlessness, candor, directness," from simplex (genitive simplicis) "simple" (see simplex). Sense of "ignorance" is from c. 1400; that of "simplicity of expression, plainness of style" is early 15c.

Middle English also had simplesse, from French, attested in English from mid-14c. in sense "humility, lack of pride," late 14c. as "wholeness, unity;" c. 1400 as "ignorance." [simplicity etymology, simplicity origin, 英语词源]
singularity (n.): c. 1400, "unusual behavior," also "singleness of aim or purpose," from Old French singulerte "peculiarity" (12c., Modern French singularité) or directly from Late Latin singularitatem (nominative singularitas) "a being alone," from singularis (see singular (adj.)). Meaning "fact of being different from others" is c. 1500. Mathematical sense of "point at which a function takes an infinite value" is from 1893. Astronomical use is from 1965.