Merriam-Webster's Collegiate® Dictionary, 11th Edition
TAB
I. noun
Usage: often attributive
Etymology: origin unknown
Date: 1607
1. a short projecting device: as, a small flap or loop by which something may be grasped or pulled, a projection from a card used as an aid in filing, a small insert, addition, or remnant, appendage , extension , a small auxiliary airfoil hinged to a control surface (as a trailing edge) to help stabilize an airplane in flight,
2. \partly short for table (I); partly from sense 1] close surveillance ; watch , a creditor's statement ; bill , check , cost ,
3. \by shortening] tabloid , tablet , a key on a keyboard especially for arranging data in columns,
II. transitive verb (tabbed; tabbing)
Date: 1872
to furnish or ornament with tabs, to single out ; designate , tabulate