How to spell COASTAR correctly?

If you meant "coaster", a possible correct suggestion could be to add the missing "e". Another possible suggestion could be to check if you meant "co-star", which refers to a lead actor in a film or show, instead of "coaster", which is a small mat or tray used for placing drinks or dishes on.

• Coastal The coastal erosion has caused damage to several beach homes.
• Coaster The roller coaster at the amusement park was the scariest ride I've ever been on.
• Costar My costar and I have great chemistry on and off the screen.

Excatally

• exact
• exacted
• exactingly
• exactly
• exacts
• executable
• exotically
• extol
• inexactly
• oxtail