Passionate tale gripping millions (6)
I believe the answer is:
stormy
'passionate' is the definition.
(I've seen this before)
'tale gripping millions' is the wordplay.
'tale' becomes 'story' ('story' can be a synonym of 'tale').
'gripping' means one lot of letters goes inside another.
'millions' becomes 'm' (abbreviation).
'story' enclosing 'm' is 'STORMY'.
(Other definitions for stormy that I've seen before include "Full of violent feeling" , "'. . . . . . Weather' (sung by Billie Holiday, say)" , "Describes weather with force 11 winds" , "Emotional" , "Turbulent or blustery" .)