Is there a term for "meltable"? [duplicate]

Yes, there is: the term for “meltable” is of course meltable.

As John Lawler observed in a comment:

Since we all understand what it means (linguists would say that meltable is "compositional", in that you can figure out the meaning of the word from the parts composing it), it IS a word. How else could we understand it?

It therefore has to be a word just as you suspected, and you have no need to consult some dictionary just to confirm your native suspicions here.

The same would be true of derived terms composed of productive affixes applied to it, like unmeltable, remeltable, unmeltability, remeltability, and so on and so forth.