Also, deal with. Be occupied or concerned with, as in Jim deals in generalities, or This book deals with idioms. The first term dates from the late 1500s, the variant from about 1300.
Do business or trade in something, as in They deal in diamonds. [Late 1500s] Also see deal with.
deal someone in. Also, deal one a hand. Include someone, give someone a share, as in I hope they'll deal me in on this new enterprise. This usage comes from card games, where to deal has meant “to distribute cards” since the 16th century. [Early 1900s]