Entry 1 sense Webster, 1913 Water sapphire /wôt'-ẽr săf'-ī-ẽr/ · Wa·ter sap·phire · IPA 01 A deep blue variety of iolite, sometimes used as a gem; -- called also saphir d'eau. 1. A deep blue variety of iolite, sometimes used as a gem; -- called also saphir d'eau.(Min.) Also: saphir d'eau