
Herbal liqueur is a sweetened spirit whose defining flavour comes from many botanicals — herbs, plants, flowers, roots and spices — macerated in or distilled with a spirit base.
Very sweet at first, turning spicy and pungent, with a markedly vegetal, herbaceous character that runs more green than comparable herbal liqueurs.
Doses run from a barspoon rinse or float up to a defining flavour measure or co-base; stirred or shaken into the build, it contributes strength, sweetness, high aroma and colour at once. Where it anchors a drink it is essentially not substitutable; as a small aromatic accent its specific signature is more expendable.
Another complex, many-botanical French herbal liqueur bottled at comparable strength and sweetness — a honeyed, rounder herbal digestif liqueur — reads as the same category role but does not reproduce the distinctive ~130-plant vegetal signature; drier substitutes can be rebalanced with simple syrup and lost strength topped with a neutral or wine-based spirit, but the proprietary aroma cannot be manufactured.
Herbal liqueurs are defined by an aromatic, often sweet many-botanical blend and are not necessarily bitter; amari are a subset defined specifically by pronounced bitterness. Both are botanical-macerated digestif liqueurs, which is why they are shelved and served alike.
The category is built from a wide blend of botanicals steeped in and/or distilled with a spirit, then sweetened; most are drunk as digestifs. Yellow Chartreuse, a French example, is produced by macerating a secret blend of said to be 130 herbs, plants and flowers in a grape-wine alcohol base, distilling, then a second maceration for colour and ageing in oak; it is the milder variant bottled around 43% ABV against Green Chartreuse's roughly 55%.
Chartreuse is a French herbal liqueur made by Carthusian monks of the Grande Chartreuse order, developed from an elixir manuscript in the early 17th century and produced at Voiron, with the recipe known at any time to only a small number of monks.

Naked & Famous
Mezcal, Herbal liqueur (e.g., Yellow Chartreuse), Aperitivo

Corpse Reviver No. 2 (Contemporary recipe)
London dry gin, Herbal liqueur (e.g., Yellow Chartreuse), Aromatized wine

Alaska (Savoy recipe)
London dry gin

Champagne Daisy
Herbal liqueur (e.g., Yellow Chartreuse)

Yellow Twilight
Chamomile cordial

Eggs-cellent
Advocaat liqueur, Cognac

Gin Daisy
London dry gin

Widows Kiss
Calvados

Alaska
Old Tom gin

Alaska (1914 recipe)
Old Tom gin

Ambrosia Cocktail
Advocaat liqueur

Brandy Daisy
Cognac

Brasil Cocktail
Cachaça

Flying Dutchman
Oude genever

Nome
London dry gin

Rum Daisy
White rum

Shanghai Gin
London dry gin, Herbal liqueur (e.g., Yellow Chartreuse), Bénédictine D.O.M. liqueur

The Optimist
White rum

Transcontinental
London dry gin

Brandy Fix
Cognac

Monkeys Go Bananas
Blended Scotch whisky

Yellow Jacket
London dry gin