Alphabetical lists used in mathematics (7)
I believe the answer is:
indices
'alphabetical lists' is the definition.
The answer and definition can be both related to communication as well as being plural nouns.
Maybe you can see an association between them that I can't see?
'in mathematics' is the wordplay.
'mathematics' becomes 'dices' (I can't justify this - if you can you should give a lot more credence to this answer).
'in'+'dices'='INDICES'
'used' acts as a link.
Can you help me to learn more?
(Other definitions for indices that I've seen before include "Catalogues" , "Mathematical symbols denoting powers" , "Files" , "Indicators; references" , "Mathematical exponents" .)