A doctor, way back, that's describing a gland (7)
I believe the answer is:
adrenal
'gland' is the definition.
(adrenal gland is a kind of gland)
'a doctor way back' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'way' becomes 'lane' (lane is a kind of way).
'back' is a reversal indicator.
'lane' back-to-front is 'enal'.
'a'+'dr'+'enal'='ADRENAL'
'that's describing a' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for adrenal that I've seen before include "Relating to glands near the kidneys" , "Relating to certain glands" , "(Gland) on the kidney" , "close to the kidneys!" , "Gland near the kidneys" .)