Drop a stone? One's required to cut weight (8)
I believe the answer is:
jettison
'drop' is the definition.
(to jettison is to drop from a ship or plane)
'a stone? one's required to cut weight' is the wordplay.
'a stone?' becomes 'jet' (type of stone).
'one's' becomes 'I's' (Roman numeral).
'required to cut' means one lot of letters goes inside another (inserted letters cut into the word).
'weight' becomes 'ton' (unit of weight).
'is' put inside 'ton' is 'tison'.
'jet'+'tison'='JETTISON'
(Other definitions for jettison that I've seen before include "Throw goods overboard, or discard what is unwanted" , "Abandon, discard" , "Eject" , "Throw things overboard to lighten ship" , "Abandon or throw overboard" .)