FU'SION, noun s as z. [Latin fusio, from fundo, fusum.]

1. The act or operation of melting or rendering fluid by heat, without the aid of a solvent; as the fusion of ice or of metals.

2. The state of being melted or dissolved by heat; a state of fluidity or flowing in consequence of heat; as metals in fusion

Watery fusion the melting of certain crystals by heat in their own water of crystallization.