Is it almost a toss up whether he’s sober? (3)
I believe the answer is:
sot
'up whether he's sober?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'is it almost a toss' is the wordplay.
'is it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
'almost' means to remove the last letter (most of the word but not all of it).
'a toss' becomes 'ot' (I can't explain this - if you can you should believe this answer much more).
'sa' with its final letter taken away is 's'.
's'+'ot'='SOT'
Can you help me to learn more?
(Other definitions for sot that I've seen before include "Lush" , "One's often intoxicated" , "drunk" , "Boozer" , "A chronic drinker" .)