Crossword Genius

Secure cheeky child the Spanish firework upset (11)

Ross

I believe the answer is:

impregnable

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

'secure' is the definition.
(I know that secure can be written as impregnable)

'cheeky child the spanish firework upset' is the wordplay.
'cheeky child' becomes 'imp' (imp is a kind of child. I am not sure about the 'cheeky' bit.).
'the spanish' becomes 'el' ('the' in Spanish).
'firework' becomes 'banger' (banger is a kind of firework).
'upset' says the letters should be written backwards.
'el'+'banger'='elbanger'
'elbanger' backwards is 'regnable'.
'imp'+'regnable'='IMPREGNABLE'

Can you help me to learn more?

(Other definitions for impregnable that I've seen before include "Unassailable" , "Not able to be overcome" , "Unable to be overcome" , "beyond doubt" , "Unable to be broken into" .)

I've seen this clue in The Times.
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