noun
four generations
Refers to a span of four generations within a family or lineage.
この家は四世にわたって続いている。
This house has been passed down for four generations.
noun
fourth-generation immigrant; yonsei
Specifically used for a person who is a fourth-generation descendant of immigrants, often in a Japanese diaspora context.
彼は日系四世としてアメリカで生まれ育った。
He was born and raised in America as a fourth-generation Japanese-American.
noun
the fourth (in a title)
Used in titles of monarchs or popes to indicate the fourth person of that name, e.g., George IV.
ジョージ四世は19世紀のイギリス国王である。
George IV was a 19th-century British king.
三世 means three generations or third-generation immigrant, while 四世 means four generations or fourth-generation.
Compound of 四 (four) and 世 (generation, world). The reading よんせい is a straightforward combination of the on'yomi readings.