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' is the 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)" .)