The word 'welling' is a transparent derivation from the verb 'well', which originates from the Old English wellan, meaning "to boil, bubble, or flow." This Old English term is rooted in the Proto-Germanic wallaną, carrying the core sense of a turbulent, rising motion, akin to boiling liquid. The addition of the nominalizing suffix '-ing', itself from Old English, converts the action into a noun describing the process or an instance of that rising motion. Thus, the literal concept of liquid bubbling up evolved seamlessly into the modern abstract meanings of any gradual surge or upwelling, whether of water from a spring or of powerful feelings like joy or sorrow.

Structure: well (to rise up) + ing (noun suffix) - well: From Old English wellan (to boil, bubble, flow), of Germanic origin. Functional role: verb root. - ing: From Old English -ung, -ing, a suffix forming nouns of action. Functional role: nominalizing suffix.