Poet laureate on the wagon train finally crosses Delaware (6)
I believe the answer is:
dryden
'poet laureate' is the definition.
'on the wagon train finally crosses delaware' is the wordplay.
'on the wagon' becomes 'dry' (no alcohol).
'finally' says to take the final letters.
'crosses' indicates putting letters inside.
'delaware' becomes 'de' (standard two letter abbrev).
The last letter of 'train' is 'n'.
'dry'+'n'='dryn'
'dryn' enclosing 'de' is 'DRYDEN'.
(Other definitions for dryden that I've seen before include "Poet laureate, 1668-1689" , "English Restoration poet" , "17th-century poet" , "English poet, d. 1700" , "Amphitryon was his" .)