early 15c., expressioun, "action of pressing out;" later "action of manifesting a feeling;" "a putting into words" (mid-15c.); from Late Latin expressionem (nominative expressio) "expression, vividness," in classical Latin "a pressing out, a projection," noun of action from past-participle stem of exprimere "represent, describe," literally "press out" (see express (v.)). Meaning "an action or creation that expresses feelings" is from 1620s. Of the face, from 1774. Occasionally the word also was used literally, for "the action of squeezing out." Related: Expressional.
word-forming element meaning "lacking, cannot be, does not," from Old English -leas, from leas "free (from), devoid (of), false, feigned," from Proto-Germanic *lausaz (cognates: Dutch -loos, German -los "-less," Old Norse lauss "loose, free, vacant, dissolute," Middle Dutch los, German los "loose, free," Gothic laus "empty, vain"), from PIE root *leu- "to loosen, divide, cut apart." Related to loose and lease.
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Harper, D. (n.d.). Etymology of expressionless. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/expressionless