Grand Hotel secures American jet (4)
I believe the answer is:
gush
'jet' is the definition.
(I know that jet can be written as gush)
'grand hotel secures american' is the wordplay.
'grand' becomes 'g' (G is short for ground as in a thousand).
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'secures' means one lot of letters goes inside another.
'american' becomes 'us' (abbreviation for United States).
'g'+'h'='gh'
'gh' going around 'us' is 'GUSH'.
(Other definitions for gush that I've seen before include "Pour forth" , "Speak effusively" , "Spout like oil-well" , "Pour out - appear overly effusive" , "Be over-effusive" .)