It's enough to make you sick! (6)
I believe the answer is:
emetic
'you sick' is the definition.
I know that 'sick' relates to this answer. I also know that both the answer and definition are singular nouns
'it's enough' is the wordplay.
'it' becomes 'e' ('e' can mean 'electronic' which is similar to 'IT').
'enough' becomes 'metic' (I can't justify this - if you can you should give a lot more credence to this answer).
'e'+'metic'='EMETIC'
'to make' acts as a link.
Can you help me to learn more?
(Other definitions for emetic that I've seen before include "medicament" , "Purgative" , "Ipecac is one" , "Medicine to make someone throw up" , "Medicine causing vomiting" .)