gomme syrup
From The Oxford Companion to Spirits & Cocktails
is the quasi-French term for gum syrup, a rich sugar syrup ostensibly thickened with gum arabic that was favored by nineteenth-century bartenders, although many of them quietly omitted the actual gum. See gum syrup.
This definition is from The Oxford Companion to Spirits & Cocktails, edited by David Wondrich (Editor-in-Chief) and Noah Rothbaum (Associate Editor).