Doctor yesterday's beginning to be teetotal (3)
I believe the answer is:
dry
'be teetotal' is the definition.
(synonyms)
'doctor yesterday's beginning' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'beginning' suggests taking the first letters.
The initial letter of 'yesterdays' is 'y'.
'dr'+'y'='DRY'
'to' acts as a link.
(Other definitions for dry that I've seen before include "Abstinent" , "Having given up drinking" , "sort of wit" , "Uninteresting" , "Sardonic" .)