Usual position, 'arsh (8)
I believe the answer is:
standard
'usual' is the definition.
(synonyms)
'position 'arsh' is the wordplay.
'position' becomes 'stand' (standing is a kind of positioning).
''arsh' becomes ''ard' ('hard' - similar in meaning - said with a cockney accent, dropping the 'H', like 'harsh' was).
'stand'+'ard'='STANDARD'
(Other definitions for standard that I've seen before include "Typical, normal" , "The usual range" , "Ceremonial flag" , "Principle" , "Criterion, touchstone" .)