outside:1.名词,"外面;外部;外边;外表;外观"eg:This coat is silk on the outside. 2.形容词,"外面的;从外面来的;外部的"eg;I'd like to see an outside world. 3.副词,"在外面;外面地;向外面"eg:The car is waiting outside. 4.介词,"在...外;除了"eg: He is outside the door. No one knows about it outside my brother.out:副词,"向外;在外;出去;出现;发生;问世;完全;消失;到终点;大声地"eg:Let's go out. He is out. The moon is out . I'm tired out. My shoes are worn out. The oil has run out. Read out ,please. have to : "不得不＂ （表示客观要求）eg: The room is too dirty. I have to clean it.must : ＂必须＂ （表示主观意志）eg: I must go now. out 副词 一般是指向外 比如 look out 有向外看的意思(当然这个词组还有个小心的意思) out of 后面加名词 表示在...的外面 outside 副词 一般是在外 比如 I play outside. 我在外面玩 还有 介词 后面加名词 outside his house 在他家外面 形容词 外面的 outside tree 户外的树 名词 在外面 outside is so hot 外面很热
追问I saw the UFO outside the window能不能换成out of the window
追答out of the window 强调状态是“出”了窗口、“离开”窗口，强调的是出的“状态”与“过程”
outside the window与 out of the window的意思相近。