Confusingly, you can substitute “some day” for situations where “someday” works — but not vice versa. The one-word adverb someday works when describing an indefinite future time (e.g., “I’d like to see him again someday”). Someday is an adverb that situates an action or event at a vague point in the future. “Someday” is incorrect in that context. It can also be used dismissively, if somebody is being pushy about getting an invitation, saying "someday" can be a way of implying "or maybe never". … “Someday” refers to an unspecified time in the future, as in “Someday my prince will come.” As two words, “some day” refers to an unspecified but specific day: The interview will be scheduled for a particular but unspecified day the following week. Someday and some day are two English terms that many writers misuse. Learn how to keep them straight in this article. Someday vs. some day. Some day is a noun phrase that refers, similarly, to a unspecified 24-hour period, also at some point in the future. Someday means “at an indefinite time in the future.” Some day refers to one day that is perhaps unknown or unspecified. Someday and some day are easy expressions to confuse because they differ by just one space. 「いつか」を辞書で調べると「One day」と「Someday」両方が出てきます。両方とも未来のある時を指しますが、そこには微妙なニュアンスの違いが生じることはご存知ですか?今日は、辞書では教えてくれない「One day」と「Someday "One day" is more specific, you are implying that there will definitely be a day when x will happen, even so it can still be a put-down - "one day but not for an unspecified while yet". Some day is two words when it refers to a single day, even if that day is unknown or not specified (e.g., “I have an appointment some day next month”).