Both stanch and staunch come from the Anglo-French estancher, meaning “to check or stop the flowing of.” Both have been in use for many hundreds of years. And most dictionaries will list them as having the exact same meaning. They are, in fact, variants of each other. But there's a catch: staunch is more commonly used as an adjective (it has several meanings in this role, including “steadfast in loyalty or principle” and "substantial"), and stanch is more commonly used as a verb (common meanings are "to check or stop the flowing of" and "to stop or check in its course"). Here are example of each in typical use:
a staunch supporter/advocate
staunch resistance/allegiance
to stanch the flow/bleeding
stanching the loss of jobs/revenue
Note that saying that something is more commonly used in some way does not necessarily mean that people who choose to use it in the less common way are wrong. There is a considerable body of evidence, from reputable sources, of staunch and stanch being used in their less common roles.
Some people will tell you that you should always keep these words apart, and if you’d like to do this you may find the following sentence of some assistance in helping you to remember the difference: "A staunch friend would help you stanch a bleeding thumb."
Alternatively, you may rely on the time-honored method of people-who-remember-things-poorly and use this limerick:
Tho’ neither stanch nor staunch must conform To rigid semantical norm Some editors will blanch, When encountering stanch If it’s used in adjective form
faithful implies unswerving adherence to a person or thing or to the oath or promise by which a tie was contracted.
faithful to her promise
loyal implies a firm resistance to any temptation to desert or betray.
remained loyal to the czar
constant stresses continuing firmness of emotional attachment without necessarily implying strict obedience to promises or vows.
constant friends
staunch suggests fortitude and resolution in adherence and imperviousness to influences that would weaken it.
a staunch defender of free speech
steadfast implies a steady and unwavering course in love, allegiance, or conviction.
steadfast in their support
resolute implies firm determination to adhere to a cause or purpose.
a resolute ally
Example Sentences
Adjective She is a staunch advocate of women's rights. He's a staunch believer in the value of regular exercise. I'm one of his staunchest supporters.
Recent Examples on the Web
Adjective
But by pinging back and forth between biography and reporting on her staunch fighting against the Sacklers, Poitras eventually collapses the distance between the two. David Fear, Rolling Stone, 14 Sep. 2022 Hadley is a staunch maximalist and vocal opponent of the Open Floor Plan. Hadley Keller, House Beautiful, 12 Sep. 2022 But Alberto Asor Rosa, a literary critic and staunch Marxist who has enjoyed a legendary status in Italy, offered a more nuanced interpretation. Anna Momigliano, The Atlantic, 12 Sep. 2022 Amid heavy casualties, logistical problems, and declining morale in Russia’s military, its performance has prompted discontent among pro-Kremlin bloggers and staunch Putin loyalists, creating new challenges for the Russian leader. Andrew Higgins, BostonGlobe.com, 12 Sep. 2022 Many Scots, though, remain staunch monarchists, and the Queen’s death has triggered an outpouring here of tributes from most political stripes. Stu Woo And Trefor Moss, WSJ, 10 Sep. 2022 The pair’s pushback received staunch criticism from in and outside the F1 paddock. Nathan Brown, The Indianapolis Star, 8 Sep. 2022 Our staunch belief in the power and sanctity of our rituals left us blind to the reality. Robin Givhan, Washington Post, 6 Sep. 2022 Still, the immigration push faces staunch opposition from some labor rights groups that don’t believe it’s the right path to immigration reform. Safia Samee Ali, NBC News, 5 Sep. 2022 See More
Word History
Etymology
Adjective
Middle English staunche, stanch "watertight, solidly made, in good repair," borrowed from Anglo-French estanc, feminine estaunche "stanched (of blood), watertight," derivative of estancher "to stop (blood from flowing), (of a wound) stop bleeding, (of water) be stanched, dry up" — more at stanch entry 1