### Clue: Tree-trunk Jack climbs for acorns, say (4)
### Answer: MAST 
 ### Explanation: Definition: Tree-trunk Jack climbs,acorns, say
 Double defn: 1. That formerly constructed from a tree-trunk, which a Jack/a seaman might climb on board a ship; and 2nd: Animal feed which could/say be made from, or including, acorns.