The base unit of counted time. Also those who come after the first — the same word for a moment and for a rank.
Latin secundus (following, second), applied twice over: the time-unit sense descends from medieval Latin's second small division of an hour, and the rank sense from the same word for whoever follows the first.
The counted units time is measured in, and, separately, those who come after whoever is first — one word doing two kinds of counting.