tick

1. 1. A cloth case for a mattress or pillow.
   2. A light mattress without inner springs.
2. Ticking.

[Middle English tikke, probably from Middle Dutch tīke, ultimately from Latin thēca, receptacle, from Greek thēkē.]

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 handwaved.

3. In the FORTH language, a single quote character.