noun
unofficial era name; apocryphal era name
A historical era name that was proposed or used locally but never officially adopted by the imperial court or government. Often encountered in academic or historical contexts.
この古文書には、正史には記録されていない逸年号が使われている。
This old document uses an unofficial era name not recorded in the official histories.
逸年号の研究は、地方の歴史を知る手がかりになる。
The study of apocryphal era names provides clues to local history.
私年号 is a near-synonym also meaning unofficial era name, often used interchangeably, though 逸年号 may emphasize the 'lost' or 'unrecorded' nuance.
Compound of 逸 (いつ, 'escape, deviate, lost') and 年号 (ねんごう, 'era name'). The exact historical derivation is uncertain; the term likely arose in modern historiography to categorize era names not found in official records.