Notices raptor has returned, having covered an enormous distance (6)
I believe the answer is:
parsec
'an enormous distance' is the definition.
(I've seen this before)
'notices raptor has returned having' is the wordplay.
'having' says the answer is hidden in the clue.
'has returned' says the letters should be written in reverse.
'cesrap' can be found hidden inside 'notices raptor'.
'cesrap' in reverse letter order is 'PARSEC'.
'covered' acts as a link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for parsec that I've seen before include "vast length" , "Unit of interstellar distance" , "nineteen million million miles" , "Three-and-a-bit light-years" , "Three+ light-years" .)