Initially creamy butter pack full (4)

I believe the answer is:

cram

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'pack full' is the definition.
'cram' can be an answer for 'pack' (synonyms). I am not sure about the 'full' bit.

'initially creamy butter' is the wordplay.
'initially' says to take the initial letters.
'butter' becomes 'ram' (I've seen this before).
The initial letter of 'creamy' is 'c'.
'c'+'ram'='CRAM'

Can you help me to learn more?

(Other definitions for cram that I've seen before include "Stuff full" , "Pack in or study hard" , "jam" , "Crowd or pack to capacity" , "Press together" .)

I've seen this clue in The Sun.

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