Definition of "diamond"

Although there are dozens of different types of gems, among the best known and most important are diamond, ruby and sapphire, emerald and other gem forms of the mineral beryl, chrysoberyl, tanzanite, tsavorite, topaz and jade.

2012 March, Lee A. Groat, “Gemstones”, in American Scientist‎, volume 100, number 2, archived from the original on 14 June 2012, page 128

Elphingston. Pearl a Chevron Diamond between three Boars Heads Eraz'd Ruby, arm'd of the first. / Eymouth. Diamond a Lyon Rampant Pearl, on a Canton of the 2d, a Cross Ruby.

1720, Francis Nichols, Rudiments of Honour, page 296

The Field is Ruby, on a Bend Topaz, three Martlets Diamond. The Armes of the most Noble and Puissant Lord, Edward Brabazon, Earl of Meath, and Baron of Atherdee in the Kingdom of Ireland. His Lordship's Atchievements are Quarterly of sixteen Coats. 1. Brabazon, as above. 2. Diamond, on a Chevron between three Pickaxes Pearl, as many Mullets Ruby, by the Name of Mosley. 3. Saphire, ten Bezants, 4, 3, 2, 1, by the Bisset.

1726, John Guillim, The Banner Display'd; Or, an Abridgment of Guillim, page 504

Pearl, an Eagle, Diamond, between three Crosses Patee, Ruby, for Morrys.

1754, John Lodge, The Peerage of Ireland; Or, a Genealogical History of the ..., page 71