Yes, they can be used as synonyms. They have a shared meaning element, but depending on context they can mean very different things.
massive, huge, giant, humongous, epic etc. missy e xx
Majestic piece of literature sry that is not very helpful
tale, saga
awesome
No, but milestone, marker or memorial are.
a huge catastrophe
In the slang term (ie "that beard is epic", "what an epic show", etc), yes. But if you look at the actual definition, no. Try heroic or bold.
cool, amazing, incredible, great, magnificent, epic
It can mean huge or gigantic.
huge or big
huge or big and giant
Gigantic, large, gargantuan, humongous.