Weak character removed from the plot (4)
I believe the answer is:
weed
'the plot' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'weak character removed' is the wordplay.
'weak' becomes 'w' (physics symbol as in W-boson).
'character' becomes 'e'.
'removed' becomes 'ed' (I can't justify this - if you can you should give a lot more credence to this answer).
'w'+'e'+'ed'='WEED'
'from' acts as a link.
Can you help me to learn more?
(Other definitions for weed that I've seen before include "Hoe to remove it" , "Got rid of water" , "Useless plant - useless person" , "Marijuana (slang)" , "Troublesome plant" .)