Sennight comes from Middle English 'sevenniht', from Old English 'seofon nihta' ('seven nights'), a compound of 'seofon' ('seven') + 'niht' ('night'). The historical chain includes Old English seofon and Old English niht. Older glosses in the chain include "sevenniht", "seofon nihta", "seven nights", and "seofon", which help explain the semantic range of the modern word. Morphologically, sennight is best read as compound and borrowing, yielding an English noun shaped by both form history and later usage. In current English it functions as a noun, with the sense "a period of seven nights; a week (archaic)". related forms include fortnight and week. The result is an English noun whose etymology preserves the older forms while supporting the word's specialized modern meaning.