Jeopardise hosting leader in Ark Royal (8)
I believe the answer is:
imperial
'royal' is the definition.
(synonyms)
'jeopardise hosting leader in ark' is the wordplay.
'jeopardise' becomes 'imperil' (synonyms).
'hosting' is an insertion indicator.
'leader in' indicates taking the first letters.
The first letter of 'ark' is 'a'.
'imperil' going around 'a' is 'IMPERIAL'.
(Other definitions for imperial that I've seen before include "Majestic - wine bottle" , "Like some rulers" , "Sovereign - old Russian gold coin - type of beard" , "Magnificent; mint --" , "Supreme, august; a beard" .)