A cause of harm to people covered in detritus, not us! (9)
I believe the answer is:
detriment
'a cause of harm' is the definition.
I can't tell whether this definition defines the answer.
'people covered in detritus not us' is the wordplay.
'people' becomes 'men' (men are people).
'covered in' means one lot of letters goes inside another.
'not' suggests deleting specific letters.
'detritus' with 'us' removed is 'detrit'.
'men' going into 'detrit' is 'DETRIMENT'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for detriment that I've seen before include "hurt" , "Possible loss" , "Harm, damage" , "State of being harmed or damaged" , "Damage, loss" .)