Define oscillator when it has to do with circadian rhythms and the suprachiasmatic nuclei?

Answer 1

An oscillator in the most general sense is nothing more than something that varies repeatably, and often in a systematic chronological manner.

In that sense, the suprachiasmatic nucleus in the brain certainly qualifies, as it secretes hormones in a regular progression - usually over a 24-hour period - even if completely isolated from external inputs.

Answer 2

The biological clock is an internal device that keeps the body's time by driving and (or) coordinating a circadian rhythm. Another name for a biological clock is an oscillator. In mammals, the suprachiasmatic nucleus (SCN) is believed to be the biological clock, and receives direct input from the retina.