adverbial N1 rare writtenliterary
よもや — surely not ~
よもや
A full written guide for よもや is on the way.
This point is mapped in the grammar tree, but its examples, formation table and usage notes haven't been written yet. The fastest way to learn it now is to meet it in real sentences inside Jengo.
See よもや in real sentences
Jengo shows よもや the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Compiled with reference to A Dictionary of Intermediate Japanese Grammar. Editorial confidence: medium.