Synonyms for Open-ended (same or very similar meaning)
WordNet sense 1 (not subject to or subjected to restriction):
unrestricted
WordNet sense 2 (not precisely determined or established; not fixed or known in advance):
indeterminate, undetermined
WordNet sense 3 (such that alteration is possible; having a marked tendency to change):
changeable, changeful
From the ODE community, based on WordNet
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