Engineers with bike to adapt for new use (7)
I believe the answer is:
recycle
'use' is the definition.
(I know this)
'engineers with bike' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'with' is a charade indicator (letters next to each other).
'bike' becomes 'cycle' (synonyms).
're'+'cycle'='RECYCLE'
'to adapt for new' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for recycle that I've seen before include "be green" , "salvage for further use" , "Use (rubbish) again" , "To use up left-overs" , "Use (waste) again" .)