"small flap," c.1600, possibly a dialectal word, of uncertain origin. Often interchangeable with tag (n.1). Cf. also Middle English tab "strap or string" (mid-15c.), Norwegian dialectal tave "piece of cloth, rag."
"account, bill, check," 1888, American English colloquial, probably a shortened form of tabulation or of tablet in the sense of "a sheet for writing on." Figurative phrase keep a tab on is recorded from 1890.
"to designate, label," 1924, perhaps an alteration of tag (v.2). Related: Tabbed; tabbing.
To keep informed about; keep watch on or over: Who's gonna keep tabs on the receipts?
[1888+; fr tab, ''bill, account'']
The bill or check for something, esp for food or drink: three-or four-hundred-dollar tabs for unpaid liquor (1942+)
A written acknowledgment of debt; iou: They're liable to go out and stick up a bank if they owe you a tab (1950s+)
[origin unknown; perhaps a shortening of tabulation]
To identify or designate; label: I tabbed him immediately as a crook
[1924+; fr tab, ''a tied-on baggage label,'' of unknown origin; perhaps an alteration of tag]
A tabloid newspaper: just be sure the other tabs and the London papers don't have track pictures either (1990s+)