You can carpe diem, or you can carp all day long.
Yes, I know my use of carpe diem as infinitive complement was grammatically incoherent, since it’s an imperative. It’s also a piece of a different language, so don’t be captious.
Which leads to an obviously important question: is carp as in ‘complain’ related to carpe diem and/or to captious? And do fish come into this? The etymology of all this turns out to be about as interwoven as a carpet, and it has threads of many words, but I’ll try to keep focused on an excerpt.
Let’s start with carpe diem. That means ‘seize the day’. The verb carpe, imperative of carpo, meaning ‘seize’ or also ‘pluck, tear, criticize, erode’, traces to Proto-Indo-European *kerp–, which has a sense of harvesting or cutting. I can almost hear those ancient iron shears clipping grape stems: “kerp, kerp, kerp.” (I am not saying that the word is originally onomatopoeic. I’m just enjoying it.)
This Latin carpo shows up in a few modern English words. One is excerpt (something cut out of something larger). Another is carpet, evidently through an association with carding wool.
Captious, on the other hand, traces to Latin capto, ‘I grasp at’ or ‘I long for’, which traces in turn to capio ‘I seize, I take’, which traces to Proto-Indo-European *keh₂p–, ‘seize, grab’, which seems very much a vocal gesture of capture, like a fish biting its prey (again, not saying that’s the origin). *keh₂p–has many descendants, including haven and Havana (and thus habanero, if you like to grab it while it’s hot), and – through the Latin forms and via French – captive, capture, catch, and chase.
So what about carp? The fish is unrelated (somehow that word carp in English is traced through Latin carpa to Gothic *karpa rather than more directly from Anglo-Saxon to Gothic). And officially the verb is unrelated, too, except there’s something fishy… The original senses came from Old Norse karpa ‘brag’, and they were senses more of just speaking or of prattling on. It is conjectured that the more recent sense (well, “recent” – it dates to the late 1300s rather than the mid-1200s) may show some influence of Latin carpo.
So this word form carp carries more voices and history than a car pool. It veritably capers. But, alas, its sense is mainly crappy. Better to seize the day and leave the cold fish behind.