I hear you asking, why is he writing a post on the origin of bandana on a blog about Thai? Well, I was recently enjoying a read through the Wikipedia page on Sanskrit loanwords in English, and found some interesting connections between English and Thai.
For those who weren't aware, Sanskrit and English are linguistic cousins. Very distant cousins, though, as part of the rather huge Indo-European language family (this means they descended from a common language--what we call "Proto-Indo-European" or PIE). And while Thai isn't part of the same family, it has an immense number of Indic (mostly Sanskrit and Pali) loanwords. Which makes for some interesting connection between English and Thai.
Which brings me to bandana. According to etymonline.com, bandana is attested in English from 1752, coming from Hindi bandhnu, a method of dyeing, from the Sanskrit badhnati "binds". The method was so-called because the cloth was tie-dyed. Go ahead, enjoy the flashback to the early 90s. Turns out the Indians were doing it three centuries earlier.
The word bandana is from the same PIE root as band in the sense "something that binds".
This is where the connection to Thai comes in. There are two cognates in Thai: พันธ- [พัน or พัน-ทะ], and พันธน- [พัน-ทะ-นะ]. Both are from the same Indic root. I'm not sure about the difference in the original language, but in Thai the former is usually a verb, meaning "tie, bind" (although it can be used as a noun to mean "obligation") and the latter is usually a nominalized form, "tying, binding; tying implement, binding implement". But really, they're basically the same word.
Looking into this causes me to wonder about the very similar word พัน. It's defined in RID99 as "to wrap around with a rope or something similar" (that's my quick, lazy translation). That sure sounds like to tie or bind, if you ask me. I looked it up in the Proto-Tai'o'Matic, which handily shows us what various scholars have written about the origins of native Thai words (as opposed to loanwords). Only one of the works, Jonsson91, claims a native origin for พัน:
Jonsson: [ *b- (A4) B16-31 ] PSW: *ban "to encircle"
I'd hardly call that conclusive, but I don't have any hard evidence to show that พัน comes from พันธ, so for now we'll put it in the "interesting correspondence that requires further investigation" category. It's the best I can do for now.