The most common and most likely answer to this crossword clue is the 8 letter word SYNONYMS
I've seen this crossword clue in Independent
S
Y
N
O
N
Y
M
S
More clues leading to the result SYNONYMS
- My sonny’s ill — tired and worn out, maybe
- Church council finishing early with rousing hymns lacking hard words such as faith, religion and belief
- Similar terms in New York my son’s arranged for accommodation
- My sons possibly absorbing extremely nerdy contents of thesauri?
- Crossword setters use these to baffle and bewilder, say
- In text, ‘an unknown value and its inverse produce equivalent terms‘
Buddy explains!

The straight part
We know that "contents of thesauri" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case contents of thesauri = synonyms.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 SYNONYMS mean?
SYNONYMS noun- (strictly) A word whose meaning is the same as that of another word.
- A word or phrase with a meaning that is the same as, or very similar to, another word or phrase.
- Any of the formal names for a taxon, including the valid name (i.e. the senior synonym).
- Any name for a taxon, usually a validly published, formally accepted one, but often also an unpublished name.
- An alternative (often shorter) name defined for an object in a database.