Doctor a Yankee for being dehydrated (3)
I believe the answer is:
dry
'being dehydrated' is the definition.
('dry' can be similar in meaning to 'dehydrated')
'doctor a yankee' is the wordplay.
'doctor' becomes 'dr' ('Dr' can be a synonym of 'doctor'**).
'a yankee' becomes 'y' (phonetic alphabet: alpha, bravo, charlie etc.).
'dr'+'y'='DRY'
'for' is the link.
(Other definitions for dry that I've seen before include "Having given up drinking" , "Not wet" , "Waterless" , "Parched" , "Not permitting alcohol" .)