英語中 first 和 second 的詞源是什麼？

顯然兩者與其對應的數詞的關係（one, two) 跟 fourth, fifth 等與對應數詞（four, five）的關係有很大差別。是否是由於 first 和 second 有不同於其他序數詞的詞源呢？

英語里的數詞基本是自源的（除了受漢語影響的諸民族語言，數詞一般都是固有詞），就是來自古日耳曼語。

first, second 跟one, two 的確不是同源的。

first 的詞根也是來自古日耳曼語，它跟英語里的fore 是一樣的，就是before, forward 裡邊的fore，表示「前面的」。
還有per, far, further 也是跟fore 同源的。
fore 的最高級就是fore+est，「最前面的」，「最重要的」，最後演變成了first。

second的詞根不是來自古日耳曼語，而是來自古羅曼語。
它的詞根跟英語里sequence, consequence 里的seque 是一樣的，表示「（次序上）跟著、接著」。

一、首先分享工具：
Online Etymology Dictionary
給大家分享一個美國比較權威的查詢詞源的網站，以前在新東方學GRE的時候老師推薦的，除了聽了很多段子之外就感覺這個網站很受用。

二、答案：
1、First

曹同學的回答部分正確，我想做詳細的解釋說明，對於同一單詞的不同詞性有可能起源是不同的。比如這個first。三種詞性，它的名詞詞性由其形容詞詞性演變而來。adj.是最常用的形式，adv.作為fore的最高級（superlative）非常少用，但存在。
Old English中寫作fyrst，源：from Proto-Germanic *furista-

first (n.)
1560s, "that which is first," from first (adj.). Meaning "first day of the month" is by 1590s. In music, "instrument or voice that takes the highest or chief part of its class," 1774. From 1909 as the name of the lowest gear in an engine. In British schools colloquial use, "highest rank in an examination," 1850.
first (adj., adv.)

Old English fyrst "foremost, going before all others; chief, principal," also (though rarely) as an adverb, "at first, originally," superlative of fore; from Proto-Germanic *furista- "foremost" (source also of Old Saxon fuirst "first," Old High German furist, Old Norse fyrstr, Danish f?rste, Old Frisian ferist, Middle Dutch vorste "prince," Dutch vorst "first," German Fürst "prince"), from PIE *pre-isto-, superlative of *pre-, from root *per- (1) "forward, through" (seehttp://etymonline.com/index.php?term=perallowed_in_frame=0).

The usual Old English superlative word was not fyrst, but forma, which shows more clearly the connection to fore. Forma became Middle English firme"first, earliest," but this has not survived.

First aid is that given at the scene, pending the arrival of a doctor. First Lady as an informal title for the wife of a U.S. president was in use by 1908, short forFirst lady of the land (by 1863 with reference to the president"s wife); the earlier title was simply Lady (1841). First name is attested from mid-13c. First base "a start" in any sense (1938) is a figurative use from baseball.

First-fruits is from late 14c. as "earliest productions of the soil;" 1590s as "first results" of any activity or endeavor. First love is from 1741 as "one"s first experience of romantic love;" 1971 as "one"s favorite occupation or pastime." First-floor is from 1660s as "story built on or just above the ground" (now U.S.); 1865 as "story built next above the ground."

2、Second
second (adj.)
"next after first," c. 1300, from Old French second, secont, and directly from Latin secundus "following, next in time or order," also "secondary, subordinate, inferior," from root of sequi "follow" (see sequel). Replaced native other in this sense because of the ambiguousness of the earlier word.Second sight is from 1610s; an etymologically perverse term, because it means in reality the sight of events before, not after, they occur. Second fiddle first attested 1809:A metaphor borrowed from a musical performer who plays the second or counter to one who plays the first or the "air." [Bartlett, "Dictionary of Americanisms," 1848]
和@曹世木討論一下Second的起源
曹同學認為Second是否起源於自古羅曼語。我覺得這個問題還可以進一步商榷。我認為Second還是起源於Latin語族。From Old French second, secont, and directly from Latin secundus。