swear by

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swear by (third-person singular simple present swears by, present participle swearing by, simple past swore by, past participle sworn by)

1. (transitive) To invoke in an oath; to swear upon.
2. (transitive, idiomatic) To trust wholeheartedly.

   I swear by my Petit Larousse when it comes to learning French.

   He swears by cream of tartar to make the meringues stiff.

   • 2016 June 24, Atlas Obscura, “A Brief History of the Referendum: From 13th century Switzerland to Brexit”, in atlasobscura.com‎^[1]:

     But while Switzerland might swear by it, elsewhere the practice has a dark history.

• Awbreys, bewrays