High official, namely one accompanying queen (6)
I believe the answer is:
vizier
'high official' is the definition.
'vizier' can be an answer for 'official' (I've seen this before). I'm not sure about the 'high' bit.
'namely one accompanying queen' is the wordplay.
'namely' becomes 'viz' (synonyms).
'one' becomes 'i' (Roman numeral).
'accompanying' means one lot of letters go next to another.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'viz'+'i'+'er'='VIZIER'
Can you help me to learn more?
(Other definitions for vizier that I've seen before include "High official in former Ottoman Empire" , "Foreign official" , "High-ranking official in some Muslim countries" , "Former Muslim official" , "Turkish bigwig" .)