Most equable ladies regularly appearing in film (7)
I believe the answer is:
mildest
'most equable' is the definition.
('mild' can be a synonym of 'equable')
'ladies regularly appearing in film' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'appearing in' means one lot of letters goes inside another.
'film' becomes 'mist' (I've seen this before**).
The alternating letters of 'ladies' are 'lde'.
'lde' inserted within 'mist' is 'MILDEST'.
(Other definitions for mildest that I've seen before include "calmer than all the others" , "Most gentle" .)