Coalition traces from PIE *h₂el- (to grow, nourish) through Latin alere and its inchoative alēscere, prefixed with co- to form coalēscere (to grow together). Medieval Latin coined the noun coalītiō, which French adopted as coalition before English borrowed it in the 1610s. It shifted from a physical sense of organic fusion to its dominant political meaning by the early 18th century.
A temporary alliance of distinct parties, persons, or states for joint action, especially in politics or warfare.
From Latin 'coalēscere' (to grow together, to unite, to coalesce), composed of 'co-' (together, with, jointly — a reduced form of 'com-') and 'alēscere' (to grow up, to be nourished), the inchoative form of 'alere' (to nourish, to rear, to cause to grow). The verbal noun 'coalītiō' (a growing together, a union) was formed in Medieval Latin and passed into French as 'coalition' before entering English in the early 17th century. The deeper PIE root of 'alere' is *h₂el- or *h₂ol- (to grow, to nourish), which also
Coalition originally described a purely physical phenomenon — things growing together or fusing, as in botany or metallurgy. Its political sense emerged a full century later, around 1710, when British pamphleteers began using it to describe alliances between parliamentary factions. The word's botanical DNA still lingers: we speak of coalitions 'forming' and 'dissolving' as though they were chemical compounds rather than political agreements.