noun, noun or participle which takes 'suru', intransitive verb
serving as a retainer; serving a lord
Historical term for serving a feudal lord or master as a retainer. Rare in modern Japanese outside historical contexts.
彼は若い頃から主君に臣事していた。
He served his lord as a retainer from a young age.
仕える is the common modern verb for serving a master or being in service, while 臣事 is a rare, formal noun/verb used mainly in historical contexts.
Compound of 臣 (retainer, subject) and 事 (to serve, matter). The exact historical derivation is uncertain; the word is associated with feudal service.