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segundo (2) m. (Noun) (time) "second"
From Latin secundus "second (in time)" but originally the numeral "second." The sense development from a number to an increment of time derives as a metaphor from the Latin idea of an hour as composed of two parts: the second and the minute. The pars minuta prima "the first small part" was the minute and the pars minuta secunda "the second small part" was the second. For a continued etymology of the word secundus, see segundo (1).