Sentence:  An idempotent element e\ne 1 of a ring is always a (two-sided) <WSD>zero divisor</WSD>, since e(1-e)=0=(1-e)e. 
Meaning of the word marked with <WSD> tags:  An element "a" of a ring "R" for which there exists some nonzero element "x" ∈ "R" such that either "ax" = 0 or "xa" = 0.