外来复数是从另一种语言借用的名词，它保留了原来的复数形式，而不是采用英语常用的-s复数结尾。

从古希腊语和拉丁语中借来的单词在英语中的外来复数形式比大多数其他外来借词保持的时间更长。

英语中的外来复数例

• “科学家根据形状将细菌[单数，细菌]分成若干组：球形细胞，标记为球菌；杆状细胞，称为杆菌；弯曲的杆状细胞，称为弧菌；螺旋状细菌。”（Sherman Hollar，《细菌、藻类和原生动物的近距离观察》，大英百科全书教育出版社，2012年）
• “这本创建和分析语言语料库的分步指南[单数，语料库]讨论了语料库语言学在语言学理论中的作用。”（Charles F.Meyer，《英语语料库语言学：导论》，剑桥大学出版社，2002年）

分开使用

英语被戏称为语言的窃贼，因为它从其他语言中借用了很多单词。但由于其他语言有自己的语法规则，这些规则通常与英语语法规则大不相同，因此这些外来词的变化和用法并不总是清晰的。当涉及到外国复数时，他们通常遵循其原语的规则。因此，对于那些希望提高英语技能或词汇量的人来说，复习希腊语和拉丁语的前缀和后缀可能会有所帮助。

"English has borrowed words from nearly every language with which it has come into contact, and particularly for nouns from Latin, Greek, Hebrew, and French, it has often borrowed their foreign plurals as well. But when loan words cease to seem 'foreign,' and if their frequency of use in English increases, they very often drop the foreign plural in favor of a regular English ​-s. Thus at any given time we can find some loan words in divided usage, with both the foreign plural (e.g., indices) and the regular English plural (e.g., indexes) in Standard use. And occasionally we’ll find a semantic distinction between the two acceptable forms, as with the awe-inspiring Hebrew cherubim and the chubby English cherubs." (Kenneth G. Wilson, The Columbia Guide to Standard American English. Columbia University Press, 1993)

拉丁语和希腊语-复数

“由于拉丁语和希腊语（复数形式）在形式上与英语的所有其他复数形式有着特殊的差异，因此它显示出被重新解释为不可数形式的趋势，或者被重新解释为单数形式，或者被解释为其自身的复数形式。这一趋势在议程上进展最快，并在criter的candelabra中得到了不同程度的接受ia、数据、媒体和现象。”

（西尔维亚·查克尔和埃德蒙·韦纳，《牛津英语语法词典》，牛津大学出版社，1994年）

主语动词与外来复数的一致性

"Well-recognized foreign plurals require plural verbs if they do not represent a singular unit. Your criteria for grading my report are unfair. Criteria, the plural form of criterion, means 'standards of rules.' This word has origins in the Greek language. Phenomena, the plural of the Greek phenomenon, is another example of plural usage. Her upper vertebrae were crushed in the accident. The singular of the Latin-derived vertebrae is vertebra." (Lauren Kessler and Duncan McDonald, When Words Collide, 8th ed. Wadsworth, 2012)