WordNet sense 1 (lacking clarity or distinctness):

dim, faint, shadowy, wispy

WordNet sense 2 (not clearly defined or easy to perceive or understand):

indistinct

WordNet sense 3 (not precisely limited, determined, or distinguished):

undefined

WordNet sense 4 (not clearly understood or expressed):

obscure

WordNet sense 5 (not clear to the mind):

unclear