Chinese languages

i've heard it for the first time a while ago. It seems akin to the particle "ze" in cantonese, which means loosely gives a sense of "only." example: wo shi kai wan xiao er yi... (by the way i don't know if that's right). "i'm only joking"

Is this right? Can someone correct me or explain it further? The characters are er2qie3 de er2 and yi3jing1 de yi3. I call it a particle cuz it seems it acts like one, but that seems weird cuz particles are supposed to be one character/syllable

eryi = literally means "only" as in I am only joking. It doesn't mean only as in he only has two cars.

why would one use "er yi" instead of zhi3shi4?

"er yi" is remainder of old written chinese。
"wo shi kai wan xiao er yi" is often seen in modern literature. In Mandarin( which i mean standard oral chinese) , it is seldom heard. Some people who want to appear to be formal or educated can use it。
It is the same as ba4le which also means er yi.