後代|こうだいkoudai[1]atamadaka (head-high)

1. nounposterity; future generations

• Synonym後世こうせいNeutralNeutral word for posterity and later ages, and also for the afterlife. More common than 「後代」; e.g. 「後世に伝える」.
• Synonym後胤こういんWrittenWritten, archaic term for descendants; stresses bloodline and does not refer to later eras.
• Synonym後裔こうえいWrittenWritten word for descendants, stressing blood lineage; e.g. 「平家の後裔」.
• Synonym後葉こうようWrittenOld written word for posterity or descendants; also a medical term for the posterior pituitary, as in 「下垂体後葉」.
• Related子孫しそんNeutralEveryday word for descendants; the focus is on a bloodline being carried on, not on a later period of time as with 「後代」.
• Related末々すえずえWrittenOld word for the distant future or for descendants; can also mean the lower classes. Rare in modern Japanese.
• Related子々孫々ししそんそんNeutralFour-character compound for one's children and grandchildren; stresses transmission from generation to generation.
• Related児孫じそんWrittenWritten term for children and grandchildren; very rare, and points to blood kin rather than a later age.
• Related末孫まっそんWrittenWritten word for descendants of distant generations; very rare, stressing a long bloodline.
• Related後昆こうこんWrittenArchaic written word for posterity; very rare — say 「子孫」 instead.
• Antonym先代せんだいNeutralThe previous generation or a former head of a family, e.g. 「先代の社長」; the opposite of 「後代」.
• Antonym前代ぜんだいNeutralFormer ages, the time before now; e.g. 「前代未聞」. The opposite of a later age.

For a later era, 「後世」 or 「後の時代」 is the usual choice; 「後代」 leans written and means the age that follows. For blood descendants the everyday word is 「子孫」, and 「子々孫々」 stresses generation after generation; most other descendant words here are written or archaic. For something unprecedented, say 「前代未聞」.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 後あとの時代じだい。