c. 1300, lenger "reside, dwell," northern England frequentative of lengen "to tarry," from Old English lengan "prolong, lengthen," from Proto-Germanic *langjan "to make long" (source also of Old Frisian lendza, Old High German lengan, Dutch lengen "to lengthen"), from *langaz- "long" (see long (adj.)).
Intransitive sense of "delay going, depart slowly and unwillingly" is from 1520s. Meaning "remain long in sickness, be near death for a time" is from 1530s. It shares verbal duties with long, prolong, lengthen. Related: Lingered; lingerer; lingering.
<a href="https://www.etymonline.com/word/lingering">Etymology of lingering by etymonline</a>
Harper, D. (n.d.). Etymology of lingering. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/lingering