noun, masculine/filtʁ/plural: philtres
philter (a kind of potion, charm, or drug intended to make the drinker fall in love with the giver)
“Dans quel philtre, dans quel vin, dans quelle tisane, / Noierons-nous ce vieil ennemi, / Destructeur et gourmand comme la courtisane, / Patient comme la fourmi?” — What wine, what drug, what philtre known of man / Will drown this ancient foe, / Ruthless and ravenous as a courtesan, / Sure as an ant, and slow?
Borrowed from Latin philtrum, itself a borrowing from Ancient Greek φίλτρον (phíltron). Unrelated to filtre.