Region of darkness initially unnerving doctor and artist (5)

I believe the answer is:

umbra

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

'region of darkness' is the definition.
'umbra' can be an answer for 'darkness' (umbra is a kind of darkness). I'm not sure about the 'region of' bit.

'initially unnerving doctor and artist' is the wordplay.
'initially' says to take the initial letters.
'doctor' becomes 'MB' (Bachelor of Medicine, Medicinae Baccalaureus).
'and' means one lot of letters go next to another.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
The initial letter of 'unnerving' is 'u'.
'u'+'mb'+'ra'='UMBRA'

Can you help me to learn more?

(Other definitions for umbra that I've seen before include "Area of total shadow" , "Dark shadow cast by earth in eclipse" , "Dark region" , "Full shadow" , "Region of shadow" .)

I've seen this clue in The Times.

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