Reference that's indicatory, with arrangement of letters? (10)
I believe the answer is:
dictionary
'reference' is the definition.
(I know that dictionary is a type of wordbook)
'indicatory with arrangement of letters?' is the wordplay.
'indicatory' can be anagrammed to 'DICTIONARY'.
However, I'm not sure how the anagram is indicated.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for dictionary that I've seen before include "Brewer's creation, say" , "Lexicon" , "Work full of meaning" , "glossary" , "reference work" .)