tick
     n 1: a metallic tapping sound; "he counted the ticks of the
          clock" [syn: {ticking}]
     2: any of two families of small parasitic arachnids with barbed
        proboscis; feed on blood of warm-blooded animals
     3: a mark indicating that something has been noted or completed
        etc.; "as he called the role he put a check mark by each
        student's name" [syn: {check mark}, {check}]
     4: a light mattress
     v 1: make a clicking or ticking sound; "The clock ticked away"
          [syn: {click}]
     2: make a sound like a clock or a timer; "the clocks were
        ticking"; "the grandfather clock beat midnight" [syn: {ticktock},
         {ticktack}, {beat}]
     3: sew; "tick a mattress" [syn: {retick}]
     4: put a check mark on or next to; "Please check each name on
        the list"; "tick off the items" [syn: {check}, {check off},
         {mark}, {mark off}, {tick off}]
Source: WordNet® 2.0

tick n. 1. A {jiffy} (sense 1). 2. In simulations, the discrete unit of
   time that passes between iterations of the simulation mechanism. In AI
   applications, this amount of time is often left unspecified, since the
   only constraint of interest is the ordering of events. This sort of AI
   simulation is often pejoratively referred to as `tick-tick-tick'
   simulation, especially when the issue of simultaneity of events with
   long, independent chains of causes is {handwave}d. 3. In the FORTH
   language, a single quote character.


Source: The Jargon File