Lout, behold, and daughter boarding helicopter (10)
I believe the answer is:
clodhopper
'lout' is the definition.
(thesaurus)
'behold and daughter boarding helicopter' is the wordplay.
'behold' becomes 'lo'.
'and' is a charade indicator (letters next to each other).
'daughter' becomes 'd'.
'boarding' is an insertion indicator.
'helicopter' becomes 'chopper' ('chopper' can be a synonym of 'helicopter').
'lo'+'d'='lod'
'lod' inserted inside 'chopper' is 'CLODHOPPER'.
(Other definitions for clodhopper that I've seen before include "Lout - heavy boot" , "Hold copper (anag)" , "Clumsy person - heavy shoe" , "Clumsy person (wearing heavy shoes?)" , "Clumsy type" .)