Wind-up has two distinct meanings:

• as an adjective, referring to mechanisms, such as clocks, music boxes and clockwork toys, which have a spring that needs to be wound up to store power for operation
• as a noun, referring to the torsion that exists in a shaft when it is subject to being twisted along its axis

As an example of the second meaning, wind-up occurs in main axle of a fixed axle vehicle if it attempts to turn a corner. The inner and outer wheels attempt to follow arcs of different radii, but the fixed axle does not allow them to rotate independently, so the axle is subject to wind-up. It is to prevent wind-up that a differential gearing mechanism is used in road vehicles. Users of Series Land Rovers are advised not to engage four-wheel drive for road use because there is no differential between the front and rear wheels. If this advice is ignored, wind-up can cause the drive shaft linking the front and rear wheels to snap.

or in an analogous sense when a person is put in a stressful situation.

As when a person is put in the situation of being deliberately led to believe one thing whilst experiencing another, usually in order to evoke an emotional response. In this usage, wind-up can be used as a noun, as in a wind-up, or as a verb, as in to wind someone up. People can also 'snap', i.e. lose their temper, if they suffer a sense of humour failure as a result of a wind-up. Prank phone calls are a type of wind-up commonly used by some radio stations.

When used as a verb, no hyphen is required. The word is also used to mean to bring to an end as in to wind up a meeting.