Tall thin plank you cut down (5)
I believe the answer is:
lanky
'tall' is the definition.
(similar in meaning)
'thin plank you cut down' is the wordplay.
'cut down' says the answer is hidden in the clue (some letters cut away to reveal the answer).
'LANKY' can be found hidden inside 'thin plank you'.
(Other definitions for lanky that I've seen before include "Ungracefully tall" , "Inelegantly tall and thin" , "Long and slender" , "Tall and gangling" , "Awkwardly long and thin" .)