also: ひとたび
noun, adverb
once; one time; on one occasion
The common reading いちど means one occurrence or one try. The reading ひとたび is more formal or literary and often means 'once' in the sense of 'once something happens'.
一度だけ彼に会ったことがある。
I have met him only once.
ひとたび始めたら、最後まで
Once I start, I see it through to the end.
noun, adverb
temporarily; for a time; for a moment
Only with reading ひとたび
Restricted to the reading ひとたび. This is an uncommon, somewhat literary adverbial use meaning that a state holds only briefly or for a limited time.
戦火はひとたび収まったが、翌年また広がった。
The fighting subsided for a time, but spread again the following year.
noun, adverb
one degree; one tone; one musical interval
Only with reading いちど
Restricted to the reading いちど. Used for one degree in measurements such as temperature or angles; in music, it can refer to a first-degree or unison-type interval.
気温が昨日より一度下がった。
The temperature fell by one degree compared with yesterday.
同じ高さの二つの音は、一度の音程と呼ばれる。
Two notes of the same pitch are called a unison interval.