Thoreau’s suggested etymology for saunterer as stemming from ‘à la Sainte Terre’ is appealing and was popular in his day, but there seems to be no support for it in dictionaries.

The derivation is usually described as uncertain but likely to be from the French s’aventurer, to venture oneself, or from ME santren, to muse, which is also given as an obsolete meaning of saunter. Pursuing santren further leads to ‘sawntrelle’, one who pretends to holiness or sainthood, with sauntering perhaps being a back formation from this. The saunterer gave the appearance of wandering about musing on holy matters. This is close to Thoreau’s derivation in meaning, but not in etymology.