Tired holding power supported by arms (8)
I believe the answer is:
weaponry
'arms' is the definition.
('weaponry' can be a synonym of 'arms')
'tired holding power supported by' is the wordplay.
'tired' becomes 'weary' ('weary' can be similar in meaning to 'tired'**).
'holding' indicates putting letters inside.
'power' becomes 'p'.
'supported by' becomes 'on'.
'p'+'on'='pon'
'weary' placed around 'pon' is 'WEAPONRY'.
(Other definitions for weaponry that I've seen before include "Big guns" , "Arsenal" , "fighting equipment" , "Arms in general" , "Armaments collectively" .)