verb/s‿ɑ̃.n‿ɛtʁ/
Used only in the simple past tense for s'en aller
“Exilés du domaine de la Couronne, les proscrits s’en furent demander asile aux provinces limitrophes[.]” — Exiled from the Crown lands, they went to request asylum in nearby provinces.
Suppletion of the verb "to go" by corresponding forms of the verb "to be" in the simple past tense is common in Romance languages (see simple past tense forms of Spanish and Portuguese ir).