20世纪

上世纪 shàngshìjì

the last century / the previous century (i.e. the 20th century, from a 21st-century viewpoint)

21世纪 èrshíyīshìjì

the 21st century (2001-2100)

世纪 shìjì HSK 3 #2,099

century

本世纪 běnshìjì #22,452

this century / the current century

中世纪 zhōngshìjì #9,880

the Middle Ages; medieval period

世纪佳缘 Shìjìjiāyuán

Jiayuan.com (Chinese marriage-oriented dating site, founded 2003 by Gong Haiyan)

过世 guòshì #4,851

to pass away / to die (euphemism)

纪录 jìlù HSK 3 #3,274

record (achievement) / to set a record; documentation

世 shì #2,998

world / generation; era / lifetime

纪念 jìniàn HSK 3 #2,882

to commemorate; to remember / memorial; souvenir