Synonyms for Indefinable (same or very similar meaning)
WordNet sense 1 (defying expression or description):
indescribable, ineffable, unspeakable, unutterable, untellable
WordNet sense 2 (defying expression):
inexpressible, unexpressible
WordNet sense 3 (not capable of being precisely or readily described; not easily put into words):
undefinable
WordNet sense 4 (not precisely limited, determined, or distinguished):
undefined, vague
From the ODE community, based on WordNet
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