indissoluble
Concise Oxford English Dictionary © 2008 Oxford University Press:
indissoluble /ˌɪndɪˈsɒljʊb(ə)l/
▶adjective unable to be destroyed; lasting.
– derivatives
indissolubility noun,
indissolubly adverb.
indissolubility noun,
indissolubly adverb.
'indissoluble' also found in these Oxford entries:

