Heard I'm in favour of a jar (7)
I believe the answer is:
amphora
'jar' is the definition.
(I know that amphora is a type of jar)
'heard i'm in favour of a' is the wordplay.
I cannot quite see how this works, but
'i'm' could be 'am' (I've seen this in other clues) and 'am' is located in the answer.
'of' could be 'o' and 'o' is found in the answer.
'a' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for amphora that I've seen before include "Classical jar for storing liquids" , "Classical two-handled jar" , "Ancient jars with two handles and narrow neck" , "Greek jug" , "Ancient tall Greek/Roman jar" .)