Indéfectible.
ETYM Latin indissolubilis: cf. French indissoluble. Related to In- not, and Dissoluble, Indissolvable.
1. Not soluble.
2. Used of decisions and contracts.
ETYM Latin insolubilis indissoluble, that can not be loosed: cf. French insoluble. Related to In- not, and Soluble, Insolvable.
1. Without hope of solution.
2. Admitting of no solution or explanation.
3. (Of a substance) Not easily dissolved.