Noticed, in retrospect, hotel has capacity for American gents
I believe the answer is:
washroom
'for american gents' is the definition.
I can't judge whether this definition defines the answer.
'noticed in retrospect hotel has capacity' is the wordplay.
'noticed' becomes 'saw'.
'in retrospect' is a reversal indicator.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'has' is a charade indicator (letters next to each other).
'capacity' becomes 'room' (I've seen this before).
'saw' reversed gives 'was'.
'was'+'h'+'room'='WASHROOM'
Can you help me to learn more?
(Other definitions for washroom that I've seen before include "US loo" , "Where Americans go" , "bog across the pond" , "Clean up place" .)