Six shot approaching Chaldean city in force (6)
I believe the answer is:
vigour
'force' is the definition.
(I know that vigour is a type of force)
'six shot approaching chaldean city' is the wordplay.
'six' becomes 'VI' (Roman numerals).
'shot' becomes 'go' (both can mean an attempt).
'approaching' means one lot of letters go next to another.
'chaldean city' becomes 'Ur' (city in the Hebrew bible).
'vi'+'go'+'ur'='VIGOUR'
'in' is the link.
(Other definitions for vigour that I've seen before include "Stamina" , "Active strength of body or mind" , "Effort, energy" , "Energy, dynamism" , "Energy, pep" .)