Real Dictionary

blur
countable noun: A blur is a shape or area which you cannot see clearly because it has no distinct outline or because it is moving very fast.
verb: If something blurs an idea or a distinction between things, that idea or distinction no longer seems clear.
verb: When a thing blurs or when something blurs it, you cannot see it clearly because its edges are no longer distinct.

blur in American English
the state of being blurred
to smear or stain without obliterating; blot; smudge
intransitive verb: to become indistinct
noun: a smudge or smear that obscures
transitive verb: to obscure or sully (something) by smearing or with a smeary substance

blur in British English
noun: something vague, hazy, or indistinct
verb: to make or become vague or less distinct