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.
This old document uses an unofficial era name not recorded in the official histories.
The study of apocryphal era names provides clues to local history.
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.