One who is called upon to answer a summons or other proceeding jointly with another.(noun)
Gnu Collaboartive International Dictionary of English: licensed under The Code Project Open License (CPOL)
Use "co-respondent" in a sentence
"She includes colorful tidbits about these figures, including the octogenarian Palmerston, who in 1863 was named as a co-respondent in a divorce suit brought by one Tom O'Kane against his wife."
"Not long after, Wellcome sued for divorce, naming Maugham as co-respondent."
"If the wife was accused of adultery, the party with whom she committed this “criminal act” was the “co-respondent.”"