Sent a message about pet (4)
I believe the answer is:
tame
'pet' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?
'sent a message about' is the wordplay.
'about' indicates the answer is hidden within the clue (the clue goes around or about the answer).
'TAME' can be found hidden inside 'sent a message'.
Can you help me to learn more?
(Other definitions for tame that I've seen before include "'Domesticated, docile (4)'" , "Flat" , "Domesticated, not wild" , "Restrained" , "Domisticated with meat" .)