Attack with a stone, possibly? (5)
I believe the answer is:
onset
'attack' is the definition.
(archaic term for a military attack)
'stone possibly?' is the wordplay.
'possibly?' indicates an anagram (I've seen 'possibly' mean this).
'stone' anagrammed gives 'ONSET'.
'with a' acts as a link.
(Other definitions for onset that I've seen before include "First signs" , "17 down [ASSAULT]" , "Initial stage; attack" , "Kick-off" , "Beginning (of disease etc)" .)