adverb, noun or participle which takes 'suru'
(not) at all; (not) in the slightest; (not) even a little
Always used with a negative predicate, typically in the set phrase びくともしない (does not budge/flinch) or similar expressions. Emphasizes complete lack of movement, reaction, or effect.
See also: びくともしない
その箱は重くて、押してもびくともしなかった。
The box was so heavy that it didn't budge even when I pushed it.
He didn't flinch at all even when he heard a scary story.