Is the 'wa' in wasabi and wakame related?


Wasabi and wakame seem to have different Japanese characters and also
different Chinese ideograms. My first guess is that the 'wa' in wasabi and
wakame is coincidence. But.

Are they related words? Mountain mustard / sea mustard? Is the wa of these
words a particle or something similar?




There are a few points of confusion here.

  * You've chosen the `particle-は` tag for your question.  
That particle is used (mainly) to mark the topic of a sentence. Particles in
general are not parts of other words.  
As you can see in the tag itself, the particle is spelled with the "ha"
hiragana は. Meanwhile, both _wasabi_ and _wakame_ are spelled with the "wa"
hiragana わ.  
→ Ultimately, neither the _wa_ in _wasabi_ nor the _wa_ in _wakame_ has
anything to do with the "wa" particle spelled は.

  * Derivationally, it's reasonable enough to ask whether the two words _wasabi_ and _wakame_ might be related. Digging around in the histories of the terms can be informative.

    * No one seems to know where the word _wasabi_ comes from. It appears in a dictionary from 918 with the phonetic kanji spelling [和]{wa}[佐]{sa}[比]{bi} (as detailed in the [Japanese Wikipedia](https://ja.wikipedia.org/wiki/%E3%83%AF%E3%82%B5%E3%83%93#%E5%90%8D%E7%A7%B0)), so we know the name is old. However, no plausible derivation has been found. Many of the various native-Japanese proposals such as those forwarded at [Gogen-Allguide](http://gogen-allguide.com/wa/wasabi.html) and at [Nihon Jiten](http://www.nihonjiten.com/data/46134.html), for example, strain credibility, considering known patterns of sound change in Japanese.  
One likely-sounding theory is that the _wasa-_ portion is [早]{wasa},
counterpart to _wase_ with a sense of "early-ripening", while the _-bi_ ending
is a shift from _mi_ with a sense of "fruit, seed, nut". However, the portion
of the wasabi plant that we use most is the root, and the plant isn't
particularly quick to ripen, so this theory doesn't fit the facts very well.
Suffice it to say that we must consider this term as an integral whole.

    * The origins of _wakame_ are also a bit murky, but comparatively much clearer. There appears to be broad agreement among the sources I've checked that the _-me_ ending is an ancient term referring to certain types of seaweed, probably cognate with the similar ancient term _mo_.  
The _waka-_ beginning, meanwhile, may refer either to young growth (as in
[若い]{wakai}, "young") or to the way the tendrils split (as in
[分かれる]{wakareru}, "to split up", from ancient root verb _waku_ ).  
See also [Gogen-Allguide](http://gogen-allguide.com/wa/wakame.html), the
[Japanese
Wikipedia](https://ja.wikipedia.org/wiki/%E3%83%AF%E3%82%AB%E3%83%A1#%E8%AA%9E%E8%AA%8C%E3%81%A8%E6%AD%B4%E5%8F%B2),
and the [English Wikipedia](https://en.wikipedia.org/wiki/Wakame).

Separately, neither food is mustard. Mustard in Japanese is _karashi_ (a noun
derived from the adjective meaning "hot, spicy"). Wasabi bears a resemblance
to horseradish in some ways, but the flavor is distinct from mustard. Wakame
may have a strong flavor, but not anything that's ever struck me as "spicy" or
"mustardy" in any way.

**Conclusions:**

  * Are _wasabi_ and _wakame_ related words?  
→ No, it does not appear that they are.

  * Is the _wa_ of these words a particle or something similar?  
→ No, the _wa_ is not a particle.

