24 across
Old
still
beer
getting
mark
with
pen
(7)
Old still beer getting mark with pen (7)
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The definition is at the beginning of the clue.
How the clue works
Old still is your definition — an alembic being that ancient bit of distillation kit. For the wordplay, chain together ALE (beer), M (mark, as an abbreviation), and BIC (you know, the pen brand) and you've got it.