Pearl finished? Be more cheerful! (4,2)
I believe the answer is:
buck up
'pearl' is the definition.
Although both the answer and definition are verbs in their base form, I cannot see how they can define each other.
'finished? be more cheerful' is the wordplay.
'finished? be more' becomes 'buck' (I can't explain this - if you can you should believe this answer much more).
'cheerful' becomes 'up' (I've seen this in other clues).
'buck'+'up'='BUCK UP'
Can you help me to learn more?
(Other definitions for buck up that I've seen before include "Informally become more cheerful or make haste - like restless horse?" , "Take heart" , "Become more serious" , "Become more cheerful like unruly horse" , "Hurry or become more cheerful - like wild horse?" .)