Lasting throughout, say, withdrawn inside (7)
I believe the answer is:
agelong
'lasting' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?
'throughout say withdrawn inside' is the wordplay.
'throughout' becomes 'along' (I've seen this before).
'say' becomes 'eg' (both can mean 'for example').
'withdrawn' says the letters should be written in reverse.
'inside' indicates putting letters inside.
'eg' in reverse letter order is 'ge'.
'along' going around 'ge' is 'AGELONG'.
Can you help me to learn more?
(Other definitions for agelong that I've seen before include "never going away?" , "Existing through history" , "over a period of many years" , "Lasting much time; lag gone (anag.)" , "permanent" .)