Feeble fathead at the bar (5)
I believe the answer is:
frail
'feeble' is the definition.
(similar in meaning)
'fathead at the bar' is the wordplay.
'fathead' becomes 'f' (head letter of 'fat').
'at' says to put letters next to each other.
'the bar' becomes 'rail' (rail is a kind of bar).
'f'+'rail'='FRAIL'
(Other definitions for frail that I've seen before include "Delicate, fragile" , "Easily shattered" , "Slight" , "Weak and infirm" , "Old woman" .)