scurrilous letter

No policeman calls an American to account for slandering the government or the president or writing scurrilous letters to editors or politicians.

Although she had taken only one quick look at that scurrilous letter, it seemed that every outrageous word was printed in letters of flame across her mind.

Other messages crawled past, mostly stsho: a dozen threats of lawsuit from irate bazaar merchants; two scurrilous letters from stsho vessels in port, impugning Chanur sanity; others were rambling.