Why WaniKani radicals have weird names
At level 9, WaniKani hands you ζ (hold) and explains it as "fingers" (ζ) plus "temple" (ε―Ί). The mnemonic, verbatim: "You need to get your fingers around a temple if you want to hold it." The image is absurd on purpose, and weeks later, when ζ comes up in reviews, the absurd image is the first thing you remember.
The problem starts the moment you step outside WaniKani. No dictionary indexes kanji by "fingers". A Japanese tutor will not know which shape you mean. These are one company's private mnemonic vocabulary, and some did not survive that company's own housecleaning. Knowing what they are for saves you from both mistakes: dismissing them as nonsense, and mistaking them for Japanese.
Two different things called "radical"
In a Japanese dictionary, every kanji is filed under exactly one classifier, its ι¨ι¦ (bushu), drawn from a list of 214 radicals inherited from the 18th-century Kangxi dictionary. Each has a Japanese name: the grass top θΉ is θε , kusakanmuri, "grass crown". The system exists to answer one question, which is where to find a kanji in a physical book.
WaniKani means something looser by the same word: any recurring shape worth a name, because the name feeds a mnemonic. Its knowledge base describes the inventory as "a combination of the traditional Kangxi list and our own creations". So the grass top becomes "flowers" (it opens θ±, θ and θΆ), and shapes the traditional list skipped get names too: "leaf" is δΈ, a two-stroke stub hiding in δΈ, ηΎ and ε€, with no Kangxi number; "fins" is γ, the splayed strokes of ε « and ε . Neither appears on a traditional radical chart.
Three kanji, side by side
ι½ is the clean case. WaniKani reads the right-side ι as "building" because it looks like a curvy letter B; the dictionary files the same shape under no. 163, ι, city. One name is a picture, the other an etymology, and here the etymology even matches the kanji's meaning. η± (heat) splits the same way on its four bottom dots: "boil" to WaniKani, the fire radical to the dictionary. ζ (teach) shows a third pattern. WaniKani reads the right side as its level 3 "winter" radical ε€; the dictionary's classifier there is ζ΅, a variant of ζ΄ (rap). The two shapes differ by one stroke, and the mnemonic system deliberately ignores it.
Where the names came from
Tofugu, the company behind WaniKani, laid out its reasoning in a 2017 article: official radical names "tend to be very general and difficult to imagine in your mind's eye", and a mnemonic built on a vague word fails. The same article adds that most Japanese people do not know the official names either.
So where a dictionary treats ζ and its squeezed left-side form ζ as variants of one hand radical, WaniKani names them separately, "hand" and "fingers", so a mnemonic always knows which shape it means. And where a kanji contains a chunk the traditional 214 never covered, WaniKani invents one. That is how you get "viking" (ιΎΈ, the horned helmet sitting on ε¦ and ε΄), "tofu" at level 12, and at level 24 "death star", whose mnemonic reads: "There is a hat covering the moon and it's holding a knife."
The 2018 renaming
The clearest proof that the names are tools came from WaniKani itself. In December 2018, after two years of work, the Content Overhaul revised radical names and rewrote mnemonics across the site: "Some will be closer to the 'traditional' radical meanings, some will be a little different, but all of them should be easier to use and remember." A community table documents roughly 80 renames: ζ went from "nailbat" to "fingers", δΊ from "boobs" to "cloud". If the names were knowledge, that would have been a catastrophe. Because they are tools, it was maintenance.
When you can forget them
Eventually the mnemonics finish their job. The kanji become atomic and the radical names quietly fall out of your head. The forum consensus, when asked whether that matters, is that it does not, as long as the kanji keep sticking. The one caveat: at higher levels visually similar kanji pile up, and a mnemonic anchored to the part that differs is still the cheapest way to tell them apart. Let the names go, but keep the habit of splitting a kanji into parts.
Other books, other names
Every mnemonic-based kanji method invented its own vocabulary, and none of them match. Heisig's Remembering the Kanji does not even call its parts radicals; they are "primitives", with Heisig's own keywords. Kenneth Henshall's A Guide to Remembering Japanese Characters runs on etymology-flavoured stories, a third vocabulary again. Enough people juggle two systems that the forum built translation tables between them. If you study from more than one source, pick a primary vocabulary and treat the rest as translations.
You do not need the traditional names to use a paper kanji dictionary, since lookup works by shape and stroke count. Where they do earn their keep: the Kanji Kentei tests them, and they are how you describe a kanji out loud to a Japanese speaker.
Should you learn the traditional names?
Not as a separate project. Unless the Kanji Kentei or regular kanji conversations with native speakers are in your near future, the hours go further in grammar or reading. And if one of those futures does arrive, you are most of the way there already: WaniKani taught you the shapes, and the shapes were the hard part. Only the labels are new.