fabulous and fantastic
Fabulous fantastic
Are they interchangeable?
Or fabulous for people (They are fabulous)
Fantastic for things (fantastic music) ?

Question

Answer

They're interchangeable, but where I am it is very rare to hear a guy say 'fabulous'. 
Most choose 'fantastic'. Here, if you're male and say 'fabulous' it  can sound effeminate. Whereas for females, I've heard both fabulous and fantastic used. Just something to be aware of.

Answer

Oh, I love your explanation.

Answer

Yes interchangeable. Fabulous can also mean fashionable. Fantastic means better than great.

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