The most common and most likely answer to this crossword clue is the 9 letter word THESAURUS
I've seen this crossword clue in The Times
T
H
E
S
A
U
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U
S
More clues leading to the result THESAURUS
- The Bull accommodates males; it offers a wide variety of terms
- Treasury so filled by Edomite king
- Isaac’s son hugged by short bird in book
- Book the man's found in house
- With nothing to lose, author uses complex reference book
- Work to provide meaningful options in other words
- Wordbook the governor’s brought into house
- Fellow's admitted to bull in work
- Reference the end for so many old beasts?
- He's enthralled by sign in book
Buddy explains!
The straight part
We know that "reference book" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reference book = thesaurus.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does THESAURUS mean?
THESAURUS noun- A publication, usually in the form of a book, that provides synonyms (and sometimes antonyms) for the words of a given language.
- A dictionary or encyclopedia.
- A hierarchy of subject headings — canonic titles of themes and topics, the titles serving as search keys.