Alienation of odd people adopted by sect regularly (12)
I believe the answer is:
Here is my best explanation:
'alienation' is the definition.
('estrangement' can be a synonym of 'alienation')
'odd people adopted by sect regularly' is the subsidiary indication.
'odd' becomes 'strange' (I've seen this before**).
'people' becomes 'men' (man is a kind of person).
'adopted by' indicates putting letters inside (I've seen this in other clues).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternate letters of 'sect' are 'et'.
'strangemen' inserted inside 'et' is 'estrangement'.
'of' is the link.
(Other definitions for estrangement that I've seen before include "alienation", "Result of splitting up", "Alienation", "lack of good relationship" and "division".)