【Obscure】 ,  【dim】 ,  【bedim】 ,  【darken】 ,  【eclipse】 ,  【cloud】 ,  【becloud】 ,  【fog】 , befog, obfuscate all mean to make dark, indistinct, or confused.

Of these terms  【obscure】 , 【dim】 , 【bedim】 , and  【darken】 all suggest the effect obtained by the lessening or the removal of illumination—the making of an object difficult to see clearly or the weakening or impairing of the ability to see with the eye or the mind.

【Obscure】 stresses the indistinctness, often concealment, of the object or idea or the unclearness of the vision or the comprehension.

【Dim】  and  【bedim】 stress the diminishing of light or of clarity, intensity, or luster or the consequent diminishing of capacity to see, distinguish, or comprehend.

【Darken】 , although like  【dim】  and  【bedim】 suggesting a diminishing of illumination, is much richer metaphorically in suggesting strongly the alteration of an object or the impairment of clear or normal vision or mental comprehension by reason of confusion, ignorance, or evil.

【Eclipse】 may stand alone in suggesting the effect of an actual astronomical 【eclipse】 , the partial or total darkening or concealment of one object by another and, hence, the overshadowing or supplanting of one object by another.

【Cloud】 , 【becloud】 , 【fog】 , befog, and obfuscate all suggest the obstruction or impairment of vision by clouds, 【fog】 , or vapor or, in extended use, the making of the mental perception or object of that perception murky or confused.  【Cloud】  and  【becloud】  stress the obscuring of the object, or the murky view of the object,  【becloud】  being somewhat more literary than  【cloud】 .

【Fog】  and befog are applied possibly more frequently than  【cloud】  and  【becloud】  to matters of the understanding or mental comprehension and usually suggest a greater obstruction or impairment of clear vision of eye and mind and, so, a greater and more unnecessary indistinctness, illogicality, or confusion;  【fog】 , however, occurs freely in both the basic sense and extended or metaphorical use while befog is uncommon in literal application.

Obfuscate, a somewhat pompous word, suggests strongly an avoidable, often willful, obscuring of an object or confusing of the mind by darkening or illogicality.