lair n.

Proto-Indo-European root meaning "to lie down, lay."

It forms all or part of: allay; anlage; belay; beleaguer; bylaw; coverlet; fellow; lager; lair; law; lawful; lawless; lawsuit; lawyer; lay (v.) "to cause to lie or rest;" ledge; ledger; lees; lie (v.2) "rest horizontally;" litter; lochia; low (adj.) "not high;" outlaw; scofflaw; stalag; vorlage.

It is the hypothetical source of/evidence for its existence is provided by: Hittite laggari "falls, lies;" Greek lekhesthai "to lie down," legos "bed," lokhos "lying in wait, ambush," alokhos "bedfellow, wife;" Latin lectus "bed;" Old Church Slavonic lego "to lie down;" Lithuanian at-lagai "fallow land;" Old Irish laigim "I lie down," Irish luighe "couch, grave;" Old English licgan "be situated, have a specific position; remain; be at rest, lie down."

late 14c., "one who or that lays" (especially stones, "a mason"), agent noun from lay (v.). Passive sense of "a thickness of some material laid over a surface" is first recorded 1610s, but because the earliest English use was in cookery this is perhaps from French liue "binding," used of a thickened sauce. Of hens from 1707. Layer cake attested from 1875.