とんでもない

Etymology
Many sources consider this to be a shift from    or.

However, citations for tondemonai precede those for todemonai by several decades (tondemonai cited to 1586–99, todemonai to 1638), pointing instead to tondemonai as the original form, and to de mo nai as a later development.

An analysis of the earliest texts indicates that this expression arose first in eastern Japanese dialects. Eastern dialects have a tendency to pre-nasalize voiced consonants, which would suggest that the initial tonde may indeed be to de (from either noun or particle ).

While the ending does appear to be, there are no historical attestations of  used separately. The term is derived from  only in relatively modern usage, such as in the now-dated expression  cited to 1950.

Despite surface similarities, the tonde here is almost certainly not derived from.

Adjective

 * 1)  unbelievable, unreasonable, extraordinary, completely unexpected, outrageous, preposterous
 * 2)  not at all
 * 1)  not at all
 * 1)  not at all

Usage notes
In older texts, this was treated as a single integral term, with the ending treated as inseparable. This was used in in constructions such as  or.

In modern usage, the ending is treated as separable, and polite constructions may replace the  ending with the negative form of the copular verb instead, such as in  or.

Derived terms

 * : outrageous, crazy