The thesaurus of synonyms and related words is fully integrated into the dictionary. Click on the thesaurus category heading under the button in an entry to see the synonyms and related words for that meaning. Past participles:arisen, been, befallen... This is the British English definition of striven.
Personally, sarcasm can mean a couple of things depending on how it is dealt out. If it is sarcastic in a funny way, that person may have a sense of humor. If it is said in a mean way, than that person is probably insecure and unhappy. IMHO!
I think Americans perfectly understand irony, but at the same time use sarcasm excessively. Everything and everybody seems to be sarcastic. Sarcasm is the default tool of humor - everything else takes a distinctive second place. Maybe it's because sarcasm is easier to use and master.