Dye and ink used in class (6)
I believe the answer is:
kidney
'class' is the definition.
(I've seen this before)
'dye and ink used' is the wordplay.
'and' is a charade indicator (letters next to each other).
'used' indicates anagramming the letters.
'dye' after 'ink' is 'inkdye'.
'inkdye' anagrammed gives 'KIDNEY'.
'in' is the link.
(Other definitions for kidney that I've seen before include "Glandular organ that removes waste matter from blood" , "Organ associated with steak" , "Organ at back of abdomen" , "Character" , "nature" .)