#staunch

First attested in the early 15th century with the specific meaning "watertight", this word comes from Old French estanche, or possibly Anglo-French estaunche, both meaning "firm or watertight". The French are probably from Vulgar Latin *stanticare, which in turn is most likely from Classical Latin stans, the present participle of stare, "to stand". The Latin is from the Proto-Indo-European root *sta-, "to stand, to be firm or make firm".

The meaning of this word was extended to include "firm, strong, substantial (of inanimate objects)" by the mid 15th century, and by the 1620s to "firm, stalwart, principled (of people)".

Although etymonline.com does not directly address the connection, my own curiosity led me to look up the very similar verb stanch, meaning "to stop the flow of (usually blood)". This verb is first attested in the early 14th century, and comes from Old French estanchier, which should look familiar. That word is a verb meaning "to cease the flow of, to drain, to hinder", and is clearly at least related to if not the source of the Old French adjective estanche, from which English staunch is said to derive.

Interestingly, etymonline.com gives different Vulgar Latin sources for the French verb and adjective, contending that the verb estanchier is from VL *stancare, which they say may be from Classical Latin stagnum, "pond or pool", but may also be from the familiar CL verb stare, "to stand".

To complicate things further, the Oxford English Dictionary Online cites *stancare as the source of both the French verb and adjective, which would make English staunch and stanch doublets. I suspect there is an even closer relationship between these two words, considering the causative relationship between them (that is, when you stanch something, you make it staunch).

Delving deeper into this question is outside the scope of this blog, though, so suffice it to say that I would not be surprised to learn that staunch in fact derives from stanch, which entered the language a century earlier. This possibility is further legitimized by the fact that in many dialects of English, the two words can be used interchangeably (that is, stanch can be used as the adjective, and staunch as the verb — indeed, the OEDO lists the verb entry as "stanch/staunch").

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Sources:

https://www.etymonline.com/word/staunch

https://www.etymonline.com/word/stanch

https://www.oed.com/dictionary/stanch_v