Sorrow registered upon return? (6)
I believe the answer is:
regret
'sorrow' is the definition.
(regret is a kind of sorrow)
'registered upon return?' is the wordplay.
I cannot quite see how this works, but
'registered' could be 'r' (abbreviation, as in registered trademark) and 'r' is found within the answer.
The remaining letters 'egret' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for regret that I've seen before include "Feeling or repentance or sorrow" , "Mourn" , "Rue - remorse" , "Feel repentant" , "Lament" .)