Ah, this looks like a nice, fair word, no? Whatever semel is, it seems soft enough, perhaps like flour (semolina? there is an obsolete word semel for a fine flour cake). The whole word flows nicely on the tongue and lips, with fricative, nasal, liquid, then stops and another liquid, and a nice open trochee/dactyl rhythm. And of course we recognize parity: it’s that word of evenness and fairness, like wage parity! No, this isn’t a word for the salmon life – you know, work like crazy swimming upstream and fighting millions of others, spawn once, and die.
Actually, it is. “Spawn once and die” pretty much sums up the sense of this word. So sorry – this is not the parity of equality. That comes from Latin par “equal”; this one comes from parare “bring forth.” And semel? Latin for “once.” Guess what: you got suckered. Oh, it looked nice enough, sounded sweet enough, so you signed on. But never mind: if you’re semelparous, you were born to do it just once. At least it’s simple – and simple echoes nicely in semel too. So do semi and semen, neither of which is etymologically related. And salmon too.
So many false leads! Well, at least you’re not subject to salmon parity, heading like the universe to a big crunch and big bang (Pacific salmon, to be specific; the Atlantic ones get several shots). But though you may not see this word often, you’re actually surrounded by semelparous things: most annual plants, for starts, and a lot of insects too, not to mention protozoans. Not us, though, and good thing: so much of the arts and crafts of humans – from countless songs and novels to a variety of appliances and applications – exists solely because of humans’ iteroparity, the converse of today’s word.