In 1999 on the Honyaku mailing list, Mark
Spahn pointed out that while the most common past tense form of the
verb 乞う is 乞うた (similar verbs include 恋う and 問う) this fact is not noted
in dictionaries. Prompted by his remark, I checked a couple of dozen
kokugo dictionaries and found none that mentioned this verb
conjugation, even though at least one dictionary had an example
sentence that included the past tense form:|
（父ハ）本堂の玄関に立って案内を乞うた ＜三島・金閣寺＞) (学研国語大辞典, 第二版, 1988)I raised the issue on a Japanese lexicography mailing list, resulting in an interesting discussion there as well.
Since then, at least two kokugo dictionaries have added notes to their entries for 乞う and some other verbs noting this irregular conjugation:
こう【請う】【乞う】… [参考] 「た（て）」につづく場合は、「請うた（て）」となる。(新選国語辞典, 第八版, 2002)I wonder if those mailing-list discussions prompted the addition of these notes.
(March 25, 2003)