expression
(not) even once; (not) ever
Always used with a negative verb to mean 'not even once' or 'never'. Emphasizes that something has not happened at all.
彼は一度も遅刻したことがない。
He has never been late, not even once.
この映画は一度も見たことがありません。
I have never seen this movie, not even once.
一度 means 'once' or 'one time' and can be used in positive sentences, while 一度も is always used with a negative verb to mean 'not even once'.
Combination of 一度 (ichido, 'once') and the inclusive particle も (mo), used with a negative predicate to express 'not even once'.