Cool kid almost losing face (5)
I believe the answer is:
chill
'cool' is the definition.
(I know that cool can be written as chill)
'kid almost losing face' is the wordplay.
'kid' becomes 'child' (synonyms).
'almost' means to remove the last letter (most of the word but not all of it).
'losing face' becomes 'l' (I can't justify this - if you can you should believe this answer much more).
'child' with its last letter removed is 'chil'.
'chil'+'l'='CHILL'
Can you help me to learn more?
(Other definitions for chill that I've seen before include "Slight cold" , "Sensation of cold or dread" , "Make cold (or frightened)" , "This disheartens" , "Preserve by cold" .)