Closely follow mother in doctrine (5)
I believe the answer is:
dogma
'doctrine' is the definition.
(I know that dogma is a type of doctrine)
'closely follow mother' is the wordplay.
'closely follow' becomes 'dog' (I've seen this in another clue).
'mother' becomes 'ma' (ma can mean mother).
'dog'+'ma'='DOGMA'
'in' acts as a link.
(Other definitions for dogma that I've seen before include "Code of belief" , "Laid down set of (religious) principles" , "Some believe it certainly" , "A religious belief" , "Inflexible doctrine" .)