Crossword Genius

Uni ensured Head left without cover (9)

Ross

I believe the answer is:

uninsured

I'm a little stuck... Click here to teach me more about this clue!

'head left without cover' is the definition.
I can't judge whether this definition defines the answer.

'uni ensured' is the wordplay.
'uni' becomes 'un' (I can't explain this - if you can you should believe this answer much more).
'ensured' becomes 'insured' ('insure' can be a synonym of 'ensure').
'un'+'insured'='UNINSURED'

Can you help me to learn more?

(Other definitions for uninsured that I've seen before include "Being without cover" , "with no policies" , "Not covered against loss" , "Not covered for losses" .)

I've seen this clue in the Sydney Morning Herald.
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