n. - A part corresponding to another part; anything which answers, or corresponds, to another; a copy; a duplicate; a facsimile.
n. - One of two corresponding copies of an instrument; a duplicate.
n. - A person who closely resembles another.
n. - A thing may be applied to another thing so as to fit perfectly, as a seal to its impression; hence, a thing which is adapted to another thing, or which supplements it; that which serves to complete or complement anything; hence, a person or thing having qualities lacking in another; an opposite.