A Thesaurus is a dictionary of synonyms and antonyms.
The word, Barbecue, has no antonyms.
try going on synonym.com you can get synonyms, antonyms and definitions.
The child had bad manners and was undisciplined in his behaviour, making him difficult to deal with.
There is no such thing, actually. You are far more likely to find synonyms of "hoof" than antonyms.
Yes you can find in dictionaries but only some
To find synonyms and antonyms you might consider looking up a word in a thesaurus
"Currently" or "Presently" are antonyms for Previously. Source: Thesaurus.com - Find Synonyms and Antonyms of words at Thesaurus.com