scanyoudaoicibaDictYouDict[scan 词源字典]
scan: [14] Latin scandere meant ‘climb’ (it has given English ascend and descend). In the postclassical period it was used metaphorically for ‘analyse the rising and falling rhythm of poetry’, and it was in this sense that it passed into English as scan. It was broadened out semantically to ‘examine’ in the 16th century, and to ‘look at widely’ in the 18th century. The Latin past participle scansus formed the basis of the noun scansiō, from which English gets scansion [17].
=> ascend, descend, scandal[scan etymology, scan origin, 英语词源]
scan (v.)youdaoicibaDictYouDict
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" (cognates: 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.)youdaoicibaDictYouDict
1706, "close investigation," from scan (v.). Meaning "act of scanning" is from 1937; sense of "image obtained by scanning" is from 1953.