clock generator and clock synthesizer

clock synthesizer:  Usually synthesize high frequency clocks from a low frequency reference clock ( Osciator or X'tal)

Clock Generator: usually contain clock synthesizer and divide the high frequency clock from synthesizer to low frequency, such that all the low frequency clocks may have "synchronous" properties.

For example:
reference clock: 10 mhz
output of synthesizer: 10 mhz
outputs of clock generator: 50mhz, 25mhz, 33mhz, 20mhz

Term clock generator is used to describe circuit or generator generally. It can be fixed or adjustable.

Clock Synthesizer is more a description of how clock signal is generated ( by synthesis ).

Synthesizer should more care about noise performance, but generator mostly do not care.