obscure, vague -- (not clearly understood or expressed; "an obscure turn of phrase"; "an impulse to go off and fight certain obscure battles of his own spirit"-Anatole Broyard; "their descriptions of human behavior become vague, dull, and unclear"- P.A.Sorokin; "vague...forms of speech...have so long passed for mysteries of science"- John Locke)
undefined, vague -- (not precisely limited, determined, or distinguished; "an undefined term"; "undefined authority"; "some undefined sense of excitement"; "vague feelings of sadness"; "a vague uneasiness")
dim, faint, shadowy, vague, wispy -- (lacking clarity or distinctness; "a dim figure in the distance"; "only a faint recollection"; "shadowy figures in the gloom"; "saw a vague outline of a building through the fog"; "a few wispy memories of childhood")
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