Don't give away a great deal about a Scottish celebration (8)
I believe the answer is:
hogmanay
'a scottish celebration' is the definition.
(I know that Hogmanay is a type of scottish celebration)
'don't give away a great deal about' is the wordplay.
'don't give away' becomes 'hog' (to hog something is keep hold of it).
'great deal' becomes 'many' (many things).
'about' means one lot of letters goes inside another.
'a' placed into 'many' is 'manay'.
'hog'+'manay'='HOGMANAY'
(Other definitions for hogmanay that I've seen before include "Scottish New Year's Eve" , "First-footing time" , "Annual celebration" , "New Year's Eve (Scots)" , "New Year's Eve in Glasgow" .)