unsmiling (adj.)

prefix of negation, Old English un-, from Proto-Germanic *un- (source also of Old Saxon, Old Frisian, Old High German, German un-, Gothic un-, Dutch on-), from PIE *n- (source of Sanskrit a-, an- "not," Greek a-, an-, Old Irish an-, Latin in-), combining form of PIE root *ne- "not." Often euphemistic (such as untruth for "lie").

The most prolific of English prefixes, freely and widely used in Old English, where it forms more than 1,000 compounds. It underwent a mass extinction in early Middle English, but emerged with renewed vigor 16c. to form compounds with native and imported words. It disputes with Latin-derived cognate in- (1) the right to form the negation of certain words (indigestable/undigestable, etc.), and though both might be deployed in cooperation to indicate shades of meaning (unfamous/infamous), typically they are not.

It also makes words from phrases (such as uncalled-for, c. 1600; undreamed-of, 1630s; uncome-at-able, 1690s; unputdownable, 1947, of a book; un-in-one-breath-utterable, Ben Jonson; etc., but the habit is not restricted to un-; such as put-up-able-with, 1812). As a prefix in telegramese to replace not and save the cost of a word, it is attested by 1936.

c. 1300, smilen, "assume a facial expression or change of features indicative of amusement and pleasure," perhaps from Middle Low German *smilen (compare Middle High German smielen) or a Scandinavian source (such as Danish smile "smile," Swedish smila "smile, smirk, simper, fawn"), from Proto-Germanic *smil-, extended form of PIE root *smei- "to laugh, smile" (source also of Sanskrit smayate "smiles;" Latvian smiêt "to laugh;" Latin mirus "wonderful," mirari "to wonder;" Old English smerian "to laugh at, scorn," Old High German smieron "to smile"). Related: Smiled; smiling; smilingly.

It gradually pushed the usual Old English word, smearcian (modern smirk), into a specific, unpleasant sense. Of the eyes, from 1759. Figuratively (of Fortune, etc.), as indicating favor or encouragement, from c. 1400. In Middle English to smile still (c. 1400) was to smile to oneself.

The saying smile and the world smiles with you is by 1884, in quotation marks, in newspaper poetry. An early second line to it was, frown, and it frowns again. [1886, credited to E.L. Ellsworth, "Cleveland Leader"]

The Romance, Celtic, and Slavic languages tend to use a diminutive of the word for "laugh" to mean "smile" (such as Latin ridere "laugh;" subridere "smile"), perhaps literally "small laugh" or "low laugh."