Soldiers besieging area take heart from corps supported by defence force (8)
I believe the answer is:
garrison
'force' is the definition.
(garrison is a kind of force)
'soldiers besieging area take' is the wordplay.
'soldiers' becomes 'grison' (I can't justify this - if you can you should believe this answer much more).
'besieging' means one lot of letters goes inside another.
'area' becomes 'a' (maths abbreviation).
'take' becomes 'r' (recipe is latin for take - r is abbreviation).
'a'+'r'='ar'
'grison' going around 'ar' is 'GARRISON'.
'heart from corps supported by defence' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for garrison that I've seen before include "Troops stationed in a town or fortress" , "Military post where troops are stationed" , "Provide (place) with troops for defence" , "army base?" , "Body of troops guarding a stronghold" .)