Heterosexual couple hiding half of what's put inside cover (7)
I believe the answer is:
sheathe
But I can't explain it at all! Could you help me understand?
(Other definitions for sheathe that I've seen before include "Put away (a sword)" , "Put (a sword) into case" , "Put into scabbard" , "Encase in protection" , "stow away safely" .)