secondyoudaoicibaDictYouDict[second 词源字典]
second: [13] Latin secundus originally meant ‘following’ – it was derived from sequī ‘follow’, source of English sequence – and only secondarily came to be used as the ordinal version of ‘two’. English acquired it via Old French second, employing it to take over part of the role of other, which until then had denoted ‘second’ as well as ‘other’.

Its noun use for ‘sixtieth of a minute’, first recorded in English in the 14th century, comes from medieval Latin secunda minuta, literally ‘second minute’ – a minute was a ‘sixtieth part’, and so a ‘second minute’ was a ‘sixtieth of a sixtieth’. Latin secundus was also used for ‘favourable’, and in this sense the verb secundāre was formed from it, meaning ‘favour’.

English acquired it via French seconder as second ‘support’ [16]. (The differently pronounced second ‘transfer to a different job’ [19] comes from the French phrase en second ‘in second rank’.)

=> sect, sequal, sequence, sue, suit[second etymology, second origin, 英语词源]
second (adj.)youdaoicibaDictYouDict
"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]
second (n.1)youdaoicibaDictYouDict
"one-sixtieth of a minute of degree," also "sixtieth part of a minute of time," late 14c. in geometry, from Old French seconde, from Medieval Latin secunda, short for secunda pars minuta "second diminished part," the result of the second division of the hour by sixty (the first being the "prime minute," now called the minute), from Latin secunda, fem. of secundus (see second (adj.)). The second hand of a clock is attested from 1759.
second (v.)youdaoicibaDictYouDict
1580s, "to support or represent in a duel, fight, etc.," from Middle French seconder, from Latin secundare "to assist, make favorable," from secundus "assisting, favorable, following, second" (see second (adj.)). The parliamentary sense is first recorded 1590s. Related: Seconded; seconding.
second (n.2)youdaoicibaDictYouDict
"assistant, supporter," 1580s, from second (v.).