Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† naphtha (napthas, Sall. ap. Prob. Cathol. 1465 P.), ae, f., = ἡ νάφθα (collat. form of ὁ νάφθας), naphtha: similis (maithae) est natura naphthae: ita appellatur circa Babyloniam et in Astacenis Parthiae profluens bituminis liquidi modo, Plin. 2, 105, 109, § 235; id. 24, 17, 101, § 158; 35, 15, 51, § 179; Amm. 23, 6, 38 (called oleum incendiarium, Veg. Mil. 4, 8 and 18; and: oleum vivum, Grat. Cyn. 434).