Port drinking at five to six? (5)
I believe the answer is:
ratio
'five to six?' is the definition.
I can't tell whether this definition defines the answer.
'port drinking at' is the wordplay.
'port' becomes 'rio' (Rio de Janeiro is a port).
'drinking' indicates putting letters inside (inserted letters are consumed or drunk).
'rio' going around 'at' is 'RATIO'.
Can you help me to learn more?
(Other definitions for ratio that I've seen before include "Mathematical relation of one thing to another" , "Relationship between two numerical quantities" , "One-to-one, maybe" , "Relativity between two quantities" , "nine-to-five, say" .)