The Gutenberg Webster's Unabridged Dictionary: Section P and Q

part in anything with an other; a partaker; an associate; a sharer.

"Partner of his fortune." Shak. Hence: (a) A husband or a wife. (b) Either one of a couple who dance together. (c) One who shares as a member of a partnership in the management, or in the gains and losses, of a business.

My other self, the partner of my life.

Milton.

2. (Law) An associate...