Uncle abroad cross about annual holiday (4)

I believe the answer is:

xmas

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

'annual holiday' is the definition.
(I've seen this before)

'uncle abroad cross about' is the wordplay.
'uncle' becomes 'sam' (Uncle Sam is an example).
'abroad cross' becomes 'x' (X is cross-shaped. I am not sure about the 'abroad' bit.).
'about' is a reversal indicator.
'sam'+'x'='samx'
'samx' written backwards gives 'XMAS'.

Can you help me to learn more?

(Other definitions for xmas that I've seen before include "annual holiday" , "Winter festival (informal)" , "present time" , "Short celebration" , "Christmas (abbrev.)" .)

I've seen this clue in The Independent.

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