Origin and history of shimmer

Middle English shinen, from Old English scinan "shed, send forth, or give out light; be radiant, be resplendent, illuminate," of persons, "be conspicuous" (class I strong verb; past tense scan, past participle scinen). This is reconstructed to be from Proto-Germanic *skeinanan (source also of Old Saxon and Old High German skinan, Old Norse and Old Frisian skina, Dutch schijnen, German scheinen, Gothic skeinan "to shine, appear"), which perhaps is from a PIE root *skai- "to shine, to gleam" (source also of Old Church Slavonic sinati "to flash up, shine").

Of smoothed or polished surfaces, "gleam, give off reflected light," late Old English. Of a person, a face, "be fair-skinned, be beautiful," c. 1200. Also used in Middle English of night when cloudless and starlit. The transitive sense of "cause to shine" is from 1580s; the meaning "to black (boots)" is from 1610s. Related: Shined (in the shoe polish sense), otherwise shone; shining.

c. 1200, flateren, flaterien, "seek to please or gratify (someone) by undue praise, praise insincerely, beguile with pleasing words," from Old French flater "to deceive; caress, fondle; prostrate, throw, fling (to the ground)" (13c.), probably from a Germanic source, perhaps from Proto-Germanic *flata- "flat" (from PIE root *plat- "to spread").

"Of somewhat doubtful etymology" [OED]. Liberman calls it "one of many imitative verbs beginning with fl- and denoting unsteady or light, repeated movement" (for example flicker, flutter). If it is related to flat the notion could be either "caress with the flat of the hand, stroke, pet," or "throw oneself flat on the ground" (in fawning adoration). The -er ending is unusual for an English verb from French; perhaps it is by influence of shimmer, flicker, etc., or from flattery.

The meaning "give a pleasing but false impression to" is from late 14c. The sense of "show (something) to best advantage" is from 1580s, originally of portraits. Related: Flattered; flattering.