The adverb 一度 "before"
一度 is used to talk about past events.
The adverb 一度 
is used to talk about a short past event.
It is placed after a subject and before a verb which is used as a predicate.
is used to talk about a short past event.
It is placed after a subject and before a verb which is used as a predicate. Pay attention
The adverb 曾 or a noun 过去 are often placed before 一度.
or a noun 过去 are often placed before 一度.Examples
这个村子曾一度是海盗藏匿之处
This village used to be a haven for pirates
zhè ge cūnzi céng yídù shì hǎidào cángnì zhī chù
人们一度认为地球是平的
Once people thought the Earth was flat
rénmen yídù rènwéi dìqiú shì píng de
他过去一度沉溺于网络游戏，不好好学习
He used to play computer games and do bad in school
tā guòqù yīdù chénnì yú wǎngluò yóuxì, bù hǎohào xuéxí
一度 is also used as a classifier with the meaning “time” in the set expression 一年一度的 .
.Examples
俱乐部一年一度的宴会将于6月3日举行
The club’s annual banquet will be held on June 3rd
jùlèbù yì nián yídù de yànhuì jiāng yú liù yuè sān rì jǔxíng