Flooding ruins fantastic hotel (6)
I believe the answer is:
inrush
'flooding ruins fantastic hotel' is the definition.
I can't judge whether this definition defines the answer.
'ruins fantastic hotel' is the wordplay.
'fantastic' is an anagram indicator (a fantastic or improbable ordering of the letters).
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'ruins' anagrammed gives 'inrus'.
'inrus'+'h'='INRUSH'
Can you help me to learn more?
(Other definitions for inrush that I've seen before include "Sudden inward flow" , "Sudden arrival or entry" , "quick entry" , "gaining sudden entry" , "Inflow" .)