• (a.) Not capable of making a will; not legally qualified or competent to make a testament.
In·tes'ta·ble adjective [ Latin intestabilis : confer French intestable . See In- not, and Testable .] (Law) Not capable of making a will; not legally qualified or competent to make a testament. Blackstone. 
not legally qualified to make a will, as an infant or a lunatic.