Perhaps liver and onions primarily contains English herb (7)
I believe the answer is:
oregano
'english herb' is the definition.
'oregano' can be an answer for 'herb' (oregano is a kind of herb). I'm unsure of the 'english' bit.
'perhaps liver and onions primarily contains' is the wordplay.
'perhaps' becomes 'eg' (for example).
'liver' becomes 'oran' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' is a charade indicator (letters next to each other).
'primarily' suggests taking the first letters.
'contains' indicates putting letters inside.
The first letter of 'onions' is 'o'.
'oran'+'o'='orano'
'eg' inserted into 'orano' is 'OREGANO'.
Can you help me to learn more?
(Other definitions for oregano that I've seen before include "Dried marjoram" , "Herb related to marjoram" , "Marjoram-like herb" , "Mediterranean herb" , "Herb - a no-goer (anag)" .)