This is a rude, old-fashioned name for a woman who shouts a lot and is often in a bad temper. It started as a job word: a fishwife was a woman who sold fish in the market. Those sellers had to call out over the noise, and English later turned the word into an insult, as if a loud angry woman “sounds like a fishwife.” Though actually, the wife piece is the old word for a woman, not “married partner” — you meet the same piece in midwife. You will almost never hear someone mean the old job now. Do not use this of a real person; it is unkind, and it also sounds like a line from an old play.