Lively beer Romanist drained (5)
I believe the answer is:
alert
'lively' is the definition.
(associated in meaning)
'beer romanist drained' is the wordplay.
'beer' becomes 'ale' (type of beer).
'drained' suggests removing the centre.
'romanist' with its middle taken out is 'rt'.
'ale'+'rt'='ALERT'
(Other definitions for alert that I've seen before include "Wide-awake and watchful" , "Awake, attentive" , "Prompt" , "Thinking and acting quickly" , "Intellectually active" .)