湿気る is both godan and ichidan. Are there other verbs like this?

Question

I recently noticed in passing that 湿気る is classified as both a godan and an ichidan verb.
For example, the past tense could be either:

しけった (godan)

or

しけた　 (ichidan).

This strikes me as being fairly unusual. Offhand, I can't think of any other verbs that have this feature. Perhaps someone knows other verbs which are classified as both godan and ichidan? Maybe someone even knows why...

Answer 1

I know this is not an optimal method, but I did a full text search on デジタル大辞泉 with 五段化, and found the following examples of ichidan-to-godan change.

• 湿気る: 下一段動詞「しけ（湿気）る」の五段化。
• 下さる: 《動詞「くだされる」（下一）の五段化》
• 抉る: 《「こじる」（上一）の五段化》
• 遣わさる: ［動ラ五（四）］「つかわされる」（下一段）の五段化。

下さる and 抉る are always godan in modern Japanese. I didn't know 遣わさ(れ)る can conjugate as a godan verb. I did a similar search on 明鏡国語辞典 and 湿気る was the only verb with the remark "五段にも活用". So I think 湿気る is a rare example of verbs that are both fully godan and fully ichidan in modern Japanese.

FWIW, I think I usually use the godan version of 湿気る. Most similar slangy verbs made from an on-yomi noun usually conjugate as a godan verb (駄弁る, 事故る, 愚痴る, ...), so the ichidan version may become less popular in the far future. This question may be related.