non-appearance n.

a prefix used freely in English and meaning "not, lack of," or "sham," giving a negative sense to any word, 14c., from Anglo-French noun-, from Old French non-, from Latin non "not, by no means, not at all, not a," from Old Latin noenum "not one" (*ne oinom, from PIE root *ne- "not" + PIE root *oi-no- "one, unique"). In some cases perhaps from Middle English non "not" (adj.), from Old English nan (see not). "It differs from un- in that it denotes mere negation or absence of the thing or quality, while un- often denotes the opposite of the thing or quality" [Century Dictionary].

late 14c., "visible state or form, figure; mere show," from Anglo-French apparaunce, Old French aparance "appearance, display, pomp" (13c.), from Latin apparentia, abstract noun from aparentem, past participle of apparere "come in sight, make an appearance," especially "be evident, be seen in public, show oneself" (see appear).

The meaning "semblance" is recorded from early 15c.; that of "action of coming into view" is by mid-15c.; that of "a coming before the public or an audience" is from 1670s. The phrase keeping up appearances is attested from 1751 (save appearances in a similar sense is by 1711; see save (v.)).