Tenpenny ballpoint? (3)

I believe the answer is:

pen

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

'ballpoint?' is the definition.
(ballpoint is a kind of pen)

'tenpenny' is the wordplay.
'PEN' is hidden in amongst the letters.
However, I'm uncertain how this is indicated.

Can you help me to learn more?

(Other definitions for pen that I've seen before include "Small enclosure" , "Write" , "International Association of poets, playwrights etc" , "Animal enclosure" , "Writing implement" .)

I've seen this clue in the Evening Standard.

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