Regarding the point about the idiom the clothes maketh the man I did a little more reading and oldest recorded reference I found is from 15th Century ...
Variations of this proverb appear earlier than Erasmus however they
appear in obscure works: “Euer maner and clothyng makyth man” (Prov.
Wisdom, 1400) and “Ffor clothyng oft maketh man.” (Peter Idley’s
Instructions to His Son, 1445).
-- Original source is The Oxford Dictionary of Proverbs
It looks to me like clothyng in both of these is singular, hence maketh was correct originally. However later when the phrase was modernized to specify clothes (i.e. plural) perhaps sometimes people (incorrectly) kept the verb maketh.
I suspect (!) this is why sometimes we hear similar pattern as in the song being discussed. I believe the phrasing in the song should be
The Words That Maken Murder
Regardless, I still love the song.