Half of line covered by green bacteria (1,4)
I believe the answer is:
e coli
'bacteria' is the definition.
Both the definition and answer are singular nouns.
Maybe they are linked in a way I don't understand?
'half of line covered by green' is the wordplay.
'half of' indicates taking half.
'covered by' means one lot of letters go next to another (on top of in a down clue).
'green' becomes 'eco' (abbreviation for ecological).
'line' halved is 'li'.
'li' after 'eco' is 'E COLI'.
Can you help me to learn more?
(Other definitions for e coli that I've seen before include "Cause of internal problem" , "Some types of this bacterium are toxic" , "Bacterium found in the gut" , "cause of ill-feeling" , "Cause of infection" .)