Son with short hair is totally chilled (10)
I believe the answer is:
stressless
'son with short hair is totally chilled' is the definition.
I can't judge whether this definition defines the answer.
'son with short hair is totally chilled' is the wordplay.
'son' becomes 'ss' (I've seen this in other clues).
'with' is an insertion indicator.
'short' means to remove the last letter.
'hair' becomes 'tress' (tress is a kind of hair).
'is totally chilled' becomes 'less' (I can't explain this - if you can you should give a lot more credence to this answer).
'tress' with its final letter taken off is 'tres'.
'ss' going around 'tres' is 'stress'.
'stress'+'less'='STRESSLESS'
Can you help me to learn more?
(Other definitions for stressless that I've seen before include "Free from pressure or tension" , "without accent?" .)