megacycle
Technical term for one million cycles per second, equivalent to megahertz (MHz). Now largely replaced by 'megahertz' in modern usage.
この無線機の周波数は100メガサイクルです。
The frequency of this radio is 100 megacycles.
メガヘルツ is the modern SI unit for frequency; メガサイクル is an older term with the same meaning, now rarely used.
Borrowed from English 'megacycle', a compound of 'mega-' (million) and 'cycle' (one complete oscillation).