Clock generator/synthesizer, Frequency generator/synthesizer. What is the difference?
Synthesizer usually is a more complex device than generator. Synthesizer consists multipliers, dividers and mixers to generate desired signal. Generator is typically a device that generates signal with fixed parameters.

Check out the ICs. For example: http://www.digikey.com/product-search/en/integrated-circuits-ics/clock-timing-clock-generators-plls-frequency-synthesizers/