From PIE *ni-sd-o- (down-sitting place) — birds' nests conceived identically across Indo-European as places for sitting down.
A structure built by a bird for incubating eggs and sheltering its young; a cozy or sheltered place; a set of similar objects that fit inside one another; to build or occupy a nest.
From Old English 'nest' (a bird's resting place, a dwelling), from Proto-Germanic *nistaz, from PIE *ni-sd-o- (a sitting-down place), a compound of *ni- (down, below) + *sed- (to sit) + nominal suffix *-o-. A nest is etymologically a 'down-sitting' — the place where a creature settles. The PIE root *sed- is one of the most productive in the language family: it gave Latin 'sedēre' (to sit), 'sella' (seat), 'residēre' (to reside), Greek 'hezesthai' (to sit), and
The word 'niche' — now meaning a specialized position — descends from Old French 'niche' (a nesting place, a recess in a wall), from Vulgar Latin '*nīdicāre' (to nest), from Latin 'nīdus' (nest). A 'niche' is etymologically a nesting spot — a recess where something sits snugly. The ecological term 'niche' preserves this perfectly: an organism's niche is the environmental 'nest' it has settled into.