Length cut from wood on smooth board (7)

'board' is the definition.
(I know that emplane is a more specific form of the action embark)

'length cut from wood on smooth' is the wordplay.
'length' becomes 'l' (abbreviation in geometry).
'cut from' is a deletion indicator.
'wood' becomes 'elm' (elm is a type of tree).
'on' says to put letters next to each other.
'smooth' becomes 'plane' (plane can mean to smooth down).
'elm' with 'l' taken away is 'em'.
'em'+'plane'='EMPLANE'