Avoid hydrogen in solar environment (4)
I believe the answer is:
shun
'avoid' is the definition.
(I know that shun is a more specific form of the action avoid)
'hydrogen in solar environment' is the wordplay.
'hydrogen' becomes 'H' (H is the chemical symbol for hydrogen).
'in' means one lot of letters goes inside another.
'solar environment' becomes 'sun' (I can't justify this - if you can you should give a lot more credence to this answer).
'h' going inside 'sun' is 'SHUN'.
Can you help me to learn more?
(Other definitions for shun that I've seen before include "Spurn; avoid" , "Deliberately avoid" , "Ostracise" , "Parade-ground language" , "'Eschew, avoid (4)'" .)