lagyoudaoicibaDictYouDict[lag 词源字典]
lag: English has three distinct words lag. The verb ‘fall behind’ [16] is perhaps of Scandinavian origin (Norwegian has lagga ‘go slowly’), although a link has been suggested with the lag of fog, seg, lag, a dialect expression used in children’s games which represents an alteration of first, second, last. Lag ‘insulate’ [19] comes from an earlier noun lag ‘barrel stave’, which was also probably borrowed from a Scandinavian language (Swedish has lagg ‘stave’); the original material used for ‘lagging’ was wooden laths.

And finally the noun lag ‘prisoner’ [19] seems to have come from an earlier verb lag, which originally meant ‘steal’, and then ‘catch, imprison’; but no one knows where this came from.
[lag etymology, lag origin, 英语词源]
lag (v.)youdaoicibaDictYouDict
"fail to keep pace," 1520s, earlier as a noun meaning "last person" (1510s), later also as an adjective (1550s, as in lag-mon "last man"), all of uncertain relationship, possibly from a Scandinavian source (compare Norwegian lagga "go slowly"), or some dialectal version of last, lack, or delay. Related: Lag; lagging. The noun meaning "retardation" is from 1855. First record of lag time is from 1951.