Boyer says:
"A fusil is a bearing in heraldry made in the form of a spindle, with its yarn or thread wound about it. Fusils are longer than lozenges, and taper or pointed at both ends."
The same author thus describes a lozenge:
"A Rhimbus, in geometry, is a figure of four equal and parallel sides, but not rectangular."
Robson says:
"Fusil, a kind of spindle used in spinning. Its formation should be particularly attended to, as few painters or engravers make a sufficient distinction between the fusil and lozenge."
Nisbet describes a lozenge to be—
"A figure that has equal sides and unequal angles, as the quarry of a glass window placed erect pointways."
He adds:
"The Latins say, 'Lozengæ factæ sunt ad modum lozangiorum in vitreis.' Heralds tell us that their use in armories came from the pavement of marble stones of churches, fine palaces and houses, cut after the form of lozenges, which pavings the French and Italians call loze and the Spaniards loza."