nonaccession means absence of accession. Lexicurio rates it Sui generis — a strength score of 95 out of 100.
Etymology
From non- + accession.
noun
- Absence of accession.“Surprisingly, even the Muslim League rejected the proposals, its objection being that the terms of nonaccession did not, unequivocally, accept the partitioning of India and the establishment of an independent Muslim state; […]”