Get drunk fast (5)
I believe the answer is:
tight
'fast' is the definition.
(I know that fast can be written as tight)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tight that I've seen before include "Close-fitting; cramped; mean" , "Drunk; giving little room" , "lack of money" , "corked?" , "reluctant to buy a round?" .)