Friendly, kindly, genial feeling.
Friendly, kindly, genial feeling — the most diffuse, outward-radiating member of the family.
The most diffuse and outward-radiating affection word, and the least tied to a specific beloved object — it describes an affable, welcoming disposition or atmosphere (“graciousness and warmth,” “a warm welcome”) more than a directed bond. Gentler and less committed than affection. Where tenderness is intimate and protective, warmth is sociable and expansive. The entry point into affection: a warm feeling can deepen into fondness, affection, or love.
warm + -th. Warm is Old English wearm, from Proto-Germanic *warmaz, of uncertain ultimate origin (possibly PIE *gwher- “to heat”).
The figurative emotional use of warm (“ardent, full of zeal”) is from the late 15c., and warm-hearted from c. 1500 — so the “warm feeling” sense grew out of physical heat via the metaphor of emotional temperature. No reliable recent-generation shift.