Elderberry liqueur is made from fermented elderberry juice. The berries grow on tall bushes and look somewhat like tiny reddish blueberries. It's possible to make your own elderberry liqueur by seeping berries in red wine or vodka. If the recipe you're contemplating calls for elderberry liqueur, substitutes are available depending on how the liqueur is used. If it's in a cocktail, use an alcohol-based substitute.
Use a berry-based liqueur such as framboise made from raspberries or crème de cassis made from currants. Other berry-based liqueurs include cherry, blackberry, blueberry and pomegranate. You won't get the true elderberry flavor, but you'll get something close to the color and the flavor of a berry.
Fruit and Elderberry Juice
Elderberries are a dark reddish-purple. If the color is critical to the recipe then using another dark purple fruit juice should work. Grape juice comes to mind, but it's sweeter than elderberry juice and more of a deep purple. Try blueberry juice or a mixture of blueberry and raspberry juice, both unsweetened if possible. If you have fresh elderberries but not elderberry liqueur, put the elderberries in a blender, strain and substitute the juice for the amount of liqueur.
Jam and Jelly
Melt elderberry jelly and replace the liqueur with an equal amount of jelly. Decrease the sugar in the recipe by an equal amount. For example, if you need 1/4 cup of elderberry liqueur, use 1/4 cup of jelly and reduce the sugar by 1/4 cup. Try elderberry jam if you don't have elderberry jelly. Jelly is made with the strained juice while jam is made with the berries and the resulting juice. Bits of berry end up in the jam.
The unflavored varieties of vodka have very little of their own taste, unlike scotch, gin, rum or other hard liquor. If the use of the elderberry liqueur is based on the necessity of alcohol then substitute vodka for the amount of liqueur. Substitute elderberry or other berry juice for half of other liquids called for in the recipe to get both the taste and alcohol. Alcohol is used to bring out flavors in cooking as well as adding its own flavor.