Adult males practised being compliant (8)
I believe the answer is:
amenable
'compliant' is the definition.
(similar in meaning)
'adult males practised' is the wordplay.
'adult' becomes 'a' (abbreviation).
'males' becomes 'men' (man is a kind of male).
'practised' becomes 'able' (I've seen this before).
'a'+'men'+'able'='AMENABLE'
'being' is the link.
(Other definitions for amenable that I've seen before include "Willing to be guided, being nameable" , "Nameable as being willing to be controlled" , "Compliant - persuadable" , "Prepared to fall in with others' plans" , "Willing to be guided or controlled" .)