Crossword Genius

Drinker is only just fine for start of evening (6)

Ross

I believe the answer is:

barfly

I'm a little stuck... Click here to teach me more about this clue!

'drinker' is the definition.
(thesaurus)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for barfly that I've seen before include "frequenter of pubs" , "pub regular" .)

I've seen this clue in The Guardian.
Want a hint initially instead of a full solution? Install my app