Father Christmas, I remembered stocking? (4)

I believe the answer is:

sire

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

'father' is the definition.
(synonyms)

'christmas i remembered stocking?' is the wordplay.
'SIRE' is hidden within the letters.
But, I'm uncertain how this is indicated.

Can you help me to learn more?

(Other definitions for sire that I've seen before include "Foal's father" , "Make children" , "Ancestor" , "Generator" , "Old form of address to king - rise to it" .)

I've seen this clue in The Guardian.

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