Unfortunately the Dictionary in question is not an online one. It is a part an parcel of my private library.
I am speaking of Chambers Dictionary of Synonyms and Antonyms (readacttor Martin H. Manser) is based on Chambers Thesarius, which itself is drawn from the extensive Chambers English Dictionary database.
Yes, it appeared too detailed to be a (free) online Dictionary. It seems like it would be worth having by many serious students of English.