Use tongue, just about spit out what may be round your mouth (8)
I believe the answer is:
lipstick
'may be round your mouth' is the definition.
I can't tell whether this defines the answer.
'use tongue just about spit out' is the wordplay.
'use tongue just' becomes 'lick' (I can't explain this - if you can you should give a lot more credence to this answer).
'about' is an insertion indicator.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'spit' with letters rearranged gives 'ipst'.
'lick' going around 'ipst' is 'LIPSTICK'.
'what' is the link.
Can you help me to learn more?
(Other definitions for lipstick that I've seen before include "offered to one's face" , "Mouth paint?" , "girl may have to face" , "Coloured cosmetic" , "Cosmetic item" .)