Soldiers coming on to extended area pull back (7)
I believe the answer is:
retract
'pull back' is the definition.
(thesaurus)
'soldiers coming on to extended area' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'coming on to' says to put letters next to each other.
'extended area' becomes 'tract' (**).
're'+'tract'='RETRACT'
(Other definitions for retract that I've seen before include "Withdraw as unjustified" , "Take back (statement)" , "Withdraw (offer, statement etc)" , "Eat one's words" , "Abjure" .)