Disinclination to act in monarch tribal, oddly (7)
I believe the answer is:
inertia
'disinclination to act' is the definition.
(I've seen this before)
'in monarch tribal oddly' is the wordplay.
'monarch' becomes 'er' (abbreviation for Elizabeth Regina).
'oddly' indicates alternate letters.
The alternate letters of 'tribal' are 'tia'.
'in'+'er'+'tia'='INERTIA'
(Other definitions for inertia that I've seen before include "Disinclination to change" , "Idling" , "Slowness to act, lassitude" , "Tendency to inactivity" , "Disinclination to respond" .)