Real Dictionary

stroboscope in American English
an instrument for studying periodic or varying motion; specif., a device using a strobe light to illuminate a moving body, machine, etc. very briefly at frequent intervals
noun: a device for studying the motion of a body, esp. a body in rapid revolution or vibration, by making the motion appear to slow down or stop, as by periodically illuminating the body or viewing it through widely spaced openings in a revolving disk

stroboscope in British English
noun: an instrument producing a flashing light, the frequency of which can be synchronized with some multiple of the frequency of rotation, vibration, or operation of an object, etc, making it appear stationary. It is used to determine speeds of rotation or vib