Liaison
mid 17th century (as a cookery term): from French, from lier ‘to bind’.
wiktionary
Borrowed from French liaison(“binding”), from Latin ligātiō (stem ligation-) (English ligation), derived from ligō(“I bind”), from Proto-Indo-European *leyǵ-(“to bind”). Doublet of ligation.
etymonline
liaison (n.)
1640s, originally in English as a cookery term for a thickening agent for sauces, from French liaison "a union, a binding together" (13c.), from Late Latin ligationem (nominative ligatio) "a binding," from past participle stem of Latin ligare "to bind" (from PIE root *leig- "to tie, bind").
Sense of "intimate relations" (especially between lovers) is from 1806. Military sense of "cooperation between branches, allies, etc." is from 1816. The meaning "one who is concerned with liaison of units, etc." is short for liaison officer (1915).
