pusher

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun One that pushes.
• noun Slang One who sells drugs illegally.

from The Century Dictionary.

• noun One who or that which pushes; one who drives forward.
• noun In mech., a stem or rod, usually with a button on the outer end, by which, from the outside of an inclosed space, some movement or result is accomplished within the space by pressing upon the button or outer extremity of the rod to push it toward the interior: as, the pusher of an electric signal or a system of electric bells, whereby an electric circuit is completed or broken.
• noun One of the levers of a type-setting machine, which, when touched on the keyboard, dislodges and pushes out a type.
• noun In railroading, an assisting locomotive placed behind a train to aid the train-engine in surmounting a steep grade. The use of a pusher over a short incline makes it possible to handle heavy trains with single engines over long levels above and below the incline.
• noun A glove-like protection made of chamois-skin or soft leather to be slipped on over the toes and instep when wearing the shoes used in running and other athletic sports.
• noun A small implement, usually of silver, used by a child, at table, to push its food upon a fork or spoon.
• noun Nautical, the seventh mast on a seven-masted vessel, the masts being named in order as follows: fore-, main-, raizzen-, jigger-, spanker-, driver-, and pusher-mast.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who, or that which, pushes.
• noun One who sells illegal drugs, esp. one who tries to convince others to use such drugs.
• noun (Railroad) a second engine attached to the rear of a train to provide extra power for climbing steep grades.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun That which pushes.
• noun An illegal drug dealer.
• noun aviation (aircraft configuration) an aircraft with the propeller behind the fuselage.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun one who intrudes or pushes himself forward
• noun a sandal attached to the foot by a thong over the toes
• noun someone who pushes
• noun a small vehicle with four wheels in which a baby or child is pushed around
• noun an unlicensed dealer in illegal drugs