Trimmed plank with three feet of cord (7)
I believe the answer is:
lanyard
'cord' is the definition.
(I know that lanyard is a type of cord)
'trimmed plank with three feet' is the wordplay.
'trimmed' says to take the centre (the edge letters are trimmed off).
'with' means one lot of letters go next to another.
'three feet' becomes 'yard' (I've seen this in another clue).
The middle letters of 'plank' are 'lan'.
'lan'+'yard'='LANYARD'
'of' acts as a link.
(Other definitions for lanyard that I've seen before include "Cord with whistle attached" , "Rope on ship's rigging" , "Cord worn around the neck by Boy Scout" , "Ribbon or cord around neck" , "Cord worn round neck" .)