Gentle drunk outside Grand Hotel (5)
I believe the answer is:
light
'gentle' is the definition.
(synonyms)
'drunk outside grand hotel' is the wordplay.
'drunk' becomes 'lit' (I've seen this in other clues).
'outside' is an insertion indicator.
'grand' becomes 'G' (synonyms).
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'g'+'h'='gh'
'lit' placed around 'gh' is 'LIGHT'.
(Other definitions for light that I've seen before include "Illumination weighs very little" , "Not heavy; understanding" , "Match - agile - easily digested" , "Illumination - not serious!" , "Weightless; lamp" .)