Through Old French, the word perplex comes from the Latin word perplexus, which could still mean "confusing" but also had side definitions of "entangled" or "intricate". Here we can chop off the prefix per-, which meant "through" (and is reconstructed as coming from the Proto-Indo-European root per, meaning "before"), leaving us with plexus, from the verb plectere, meaning "to weave". You can see there that the "entangled" etymology was most prominent going back. Plectere, through Proto-Italic plekto, may be derived from Proto-Indo-European plek, meaning "weave" or, alternatively, "to fold". So, furthest back, perplex means "before folding". Usages of perplex in every context have been decreasing since the nineteenth century, but perplexed tops the list as the most utilized form of the word. The same pattern is echoed in both Google Trends and NGrams.
Hello! I'm Adam Aleksic, a sophomore studying linguistics and government at Harvard University, where I founded the Harvard Undergraduate Linguistics Society. I also have disturbing interests in politics, vexillology, geography, board games, conlanging, and law.