(So many questions lately, sorry. Saturday I go on holiday!)
A gatecrasher is a person who turns up uninvited at a party or function.
汉语说:不速之客
速: speed 不速之客: no speed guest = gatecrasher ??
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Sign up to join this community多功能成语词典 explains:
解释 速:邀请。指未经邀请而突然自己来的客人。
and also gives the note:
提示 “速"不要解释成“速度"或“迅速"。
A Student's Dictionary of Classical and Medieval Chinese also notes that 速 has the meanings
2 lead to, induce to; beckon toward; invite.
汉语大词典 also notes this meaning, with many examples
5 召, 请。
《诗·小雅·伐木》 既有肥羜, 以速諸父。
郑玄 笺 速, 召也。
《文选·张衡〈思玄赋〉》 速燭龍令執炬兮, 過 鍾山 而中休。
旧注 速, 徵也。
清 顾禄 《清嘉录·冬至大如年》 是夜, 人家更速燕飲, 謂之節酒。
杨树达 《〈凌虚岛〉小说序》 近者得君札, 速余序君書。
It’s not that 速 came to mean invite - but rather that it meant this as early as I Ching, which came out roughly 1100 BC - over three thousand years ago:
《周易·需》:“有不速之客三人来。"