Reach base by part of camp (6)
I believe the answer is:
extent
'reach' is the definition.
(thesaurus)
'base by part of camp' is the wordplay.
'base' becomes 'e' (I've seen this in other clues).
'by' becomes 'x' (multiplication sign).
'part of camp' becomes 'tent' (I've seen this before).
'e'+'x'+'tent'='EXTENT'
(Other definitions for extent that I've seen before include "Scope, area" , "Length" , "Area of coverage" , "Degree - amount - scope" , "Measure" .)