Liquid that's first injected into chopped lemon (6)
I believe the answer is:
molten
'liquid' is the definition.
('molten' can be similar in meaning to 'liquid')
'that's first injected into chopped lemon' is the wordplay.
'first' suggests taking the first letters.
'injected into' is an insertion indicator.
'chopped' indicates anagramming the letters.
The first letter of 'that' is 't'.
'lemon' is an anagram of 'molen'.
't' inserted inside 'molen' is 'MOLTEN'.
(Other definitions for molten that I've seen before include "State of moving lava" , "hot but ready to pour" , "Liquid (of metal)" , "Liquefied by heat" , "Reduced to liquid form by heating" .)