Cold, simple chemical substance losing one electron at first becomes mild (7)
I believe the answer is:
clement
'mild' is the definition.
(similar in meaning)
'cold simple chemical substance losing one electron at first' is the wordplay.
I cannot quite understand how this works, but
'cold' could be 'c' (eg on taps) and 'c' is found in the answer.
'substance' could be 'n' (N is an example) and 'n' is present in the answer.
'one' could be 'me' (a setter might use 'one' to humourously mean 'me') and 'me' is located in the answer.
'electron' could be 'e' (abbreviation in physics) and 'e' is found in the answer.
This explanation may well be incorrect...
'becomes' acts as a link.
Can you help me to learn more?
(Other definitions for clement that I've seen before include "opponent for Winston" , "Mild or balmy" , "Fine" , "(Of weather) mild, lenient" , "gentle approach" .)