indwelling (n.)

a Middle English merger of Old English in (prep.) "in, into, upon, on, at, among; about, during;" and Old English inne (adv.) "within, inside," from Proto-Germanic *in (source also of Old Frisian, Dutch, German, Gothic in, Old Norse i), from PIE root *en "in." The simpler form took on both senses in Middle English.

Sense distinction between in and on is from later Middle English, and nuances in use of in and at still distinguish British and American English (in school/at school). Sometimes in Middle English shortened to i.

The noun sense of "influence, access (to power or authorities)," as in have an in with, is first recorded 1929 in American English. to be in for it "certain to meet with something unpleasant" is from 1690s. To be in with "on friendly terms with" is from 1670s. Ins and outs "intricacies, complications of an action or course" is from 1660s. In-and-out (n.) "copulation" is attested from 1610s.

Old English dwellan "to lead into error, deceive, mislead," related to dwelian "to be led into error, go wrong in belief or judgment," from Proto-Germanic *dwaljana "to delay, hesitate," *dwelana "go astray" (source also of Old Norse dvelja "to retard, delay," Danish dvæle “to linger, dwell,” Swedish dväljas “to dwell, reside;” Middle Dutch dwellen "to stun, perplex;" Old High German twellen "to hinder, delay") from PIE *dhwel-, extended form of root *dheu- (1) "dust, cloud, vapor, smoke" (also forming words with the related notions of "defective perception or wits").

The apparent sense evolution in Middle English was through "to procrastinate, delay, be tardy in coming" (late 12c.), to "linger, remain, stay, sojourn," to "make a home, abide as a permanent resident" (mid-14c.). From late 14c. as "remain (in a certain condition or status)," as in phrase dwell upon "keep the attention fixed on." Related: Dwelled; dwelt (for which see went); dwells.

It had a noun form in Old English, gedweola "error, heresy, madness." Also compare Middle English dwale "deception, trickery," from Old English dwala or from a Scandinavian cognate (such as Danish dvale "trance, stupor, stupefaction"); dwale survived into late Middle English as "a sleeping potion, narcotic drink, deadly nightshade."