Wiktionary
material breach
n. 1 (context legal English) a breach of contract sufficiently serious to destroy the contract 2 a breach of a treaty which releases other parties from any obligation under it
WordNet
material breach
n. a breach serious enough to destroy the value of the contract and to give a basis for an action for breach of contract
Usage examples of "material breach".
Any such communication by CONTRACTOR shall be deemed to be a material breach of CONTRACT by CONTRACTOR.