once in a while

日豪：
這兩句的意思是很久一次地, 亦即不常地(infrequently), 偶爾地(sporadically),間中地(occasionally)等, 其表達的意思是完全一樣, 但句子的結構則不一樣。
once 一字可作副詞(adverb), 但亦可作名詞(noun)用。如
My sister comes to see me once in a while.很明顯once in a while是用作副詞短語(adverb phrase)以加上某些描述在上面動詞令句子意思完滿而可解作
我的姐姐間中會來探望我。意思和 My sister comes to see me every once in
a while.一樣, 但every once in a while中的every只可作形容詞之用, 而形容詞只能用以形容事物, 在這裏它就是用作形容解作'一次' 的名詞(once)了。相若的句子如 My mother makes cookies once in a while.和 My mother makes
cookies every once in a while.同樣是解作我母親偶爾會做曲奇士餅, 但第二句子中的 once 亦作名詞用, 換句話說, 兩句意思一樣, 句子用字結構不同而已。

“every” is a determiner 限定詞, used to say how often something happens or is done = 每逢, 每隔 + 時段/ 距離 e.g. We see each other every other week. e.g. He smiles every time I see himonce in a while= occasionally 偶爾地, 閒或every + once in a while --à every強調每次/每逢(偶爾/間或) ,,,都同樣發生...

有時
they are the same meaning!!

1.有時
.
He went to see them once in a while. 他有時去探望他們。
應該冇分別