noun, noun or participle which takes 'suru', transitive verb
restoration to the emperor; returning (power) to the emperor
Historical term, most famously used in 大政奉還 (Taisei Hōkan), the return of political power to the Emperor in 1867. Rarely used outside this context.
大政奉還は江戸幕府が政権を朝廷に返上した出来事だ。
The Taisei Hōkan was the event in which the Edo shogunate returned political power to the Imperial Court.
返還 is a general term for returning something (e.g., territory, rights), while 奉還 specifically implies returning something to a superior, especially the emperor.
Compound of 奉 (ほう, 'to offer respectfully') and 還 (かん, 'to return'). The exact historical derivation is uncertain, but the word is strongly associated with the Meiji Restoration.