German prince regularly rattled those entitled to vote (10)
I believe the answer is:
electorate
'those entitled to vote' is the definition.
(I've seen this before)
'german prince regularly rattled' is the wordplay.
'german prince' becomes 'elector' (I've seen this before).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'rattled' are 'ate'.
'elector'+'ate'='ELECTORATE'
(Other definitions for electorate that I've seen before include "Those entitled to vote" , "Voters in general" , "Constituency" , "Voters collectively" , "Voters as a whole" .)