Long-lasting (7)
I believe the answer is:
durable
This clue is a double definition.
'long' is the first definition.
(similar in meaning)
'lasting' is the second definition.
(I know that lasting can be written as durable)
(Other definitions for durable that I've seen before include "Rugged; long-lasting" , "Firm" , "Likely to last" , "Hardy" , "Good" .)