Scan
late Middle English (as a verb in scan (sense 3 of the verb)): from Latin scandere ‘climb’ (in late Latin ‘scan (verses)’), by analogy with the raising and lowering of one's foot when marking rhythm. From ‘analyse (metre)’ arose the senses ‘estimate the correctness of’ and ‘examine minutely’, which led to ‘look at searchingly’ (late 18th century).
wiktionary
From Middle English scannen(“to mark off verse to show metrical structure”), from earlier *scanden, from Late Latinscandere(“to scan verse”), from Classical Latin scandō(“I climb, rise, mount”).
etymonline
scan (v.)
late 14c., "mark off verse in metric feet," from Late Latin scandere "to scan verse," originally, in classical Latin, "to climb, rise, mount" (the connecting notion is of the rising and falling rhythm of poetry), from PIE *skand- "to spring, leap, climb" (source also of Sanskrit skandati "hastens, leaps, jumps;" Greek skandalon "stumbling block;" Middle Irish sescaind "he sprang, jumped," sceinm "a bound, jump").
Missing -d in English is probably from confusion with suffix -ed (see lawn (n.1)). Sense of "look at closely, examine minutely (as one does when counting metrical feet in poetry)" first recorded 1540s. The (opposite) sense of "look over quickly, skim" is first attested 1926. Related: Scanned; scanning.
scan (n.)
1706, "close investigation," from scan (v.). Meaning "act of scanning" is from 1937; sense of "image obtained by scanning" is from 1953.
