Here's what rhymes with unquantifiable.

Consider these alternatives

unproved / used unoriginal / original insubstantial / sample quantifying / dying imprecision / given emotionalism / given idealization / relation mitigates / states underappreciated / dated unspecific / specific unrealised / realized unidentifiable / viable mitigations / relations unsuspected / subjected unverified / side quantify / high minimising / living unfathomable / fashionable egoistic / characteristic