See rage held back on the inside, strangely (6)
I believe the answer is:
eerily
'strangely' is the definition.
(I've seen this before)
'see rage held back on the inside' is the wordplay.
'see' becomes 'ely' (example where cathedral located in diocese).
'rage' becomes 'ire' (I've seen this before).
'held back' is a reversal indicator.
'on the inside' is an insertion indicator.
'ire' back-to-front is 'eri'.
'ely' placed around 'eri' is 'EERILY'.
(Other definitions for eerily that I've seen before include "Weirdly, frighteningly" , "In a strange and frightening way" , "In a strangely frightening manner" , "In spooky or ghostly manner" , "In a strange and frightening manner" .)