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once

1 once /ˈwʌns/ adverb
1 once
/ˈwʌns/
adverb
Britannica Dictionary definition of ONCE
: one time only
: at any one time : ever
: at some time in the past
sometimes used in combination

once again/more

: for another time : one more time : again

once and for all

: now and for the last time

once bitten, twice shy

see 1bite

once in a blue moon

see blue moon

once in a while

: sometimes but not often : occasionally

once upon a time

: at some time in the past
Once upon a time is the traditional way to begin a fairy tale.
2 once /ˈwʌns/ noun
2 once
/ˈwʌns/
noun
Britannica Dictionary definition of ONCE
[noncount]
: one single time

at once

: at the same time
: right away : without delay : immediately
3 once /ˈwʌns/ conjunction
3 once
/ˈwʌns/
conjunction
Britannica Dictionary definition of ONCE
: at the moment when : as soon as