おいoi
1.

A male child of one's sibling or sibling's spouse, who is considered a relative in the family lineage.

2.

The son of one's brother or sister, representing a familial connection that signifies both lineage and social relationship within the family structure.

Example:

私のおいは卵に対してアレルギー体質だ。

おいoikoおいっこ甥子oikkoおいご甥子oigo
1.

A male child of one’s sibling or sibling-in-law, often considered a younger relative in the family structure.

2.

A young boy or man who is specifically related to someone through their brother or sister, highlighting a familial bond between generations.

3.

A person who occupies the familial role of a nephew, typically characterized by a relationship with an uncle or aunt that may involve mentorship or care.

おいご甥御oigo
1.

A respectful term used to refer to someone else's nephew, often used with the honorific suffix "san."

2.

A formal way to acknowledge or address the nephew of another person, indicating a sense of politeness and distance.