lambswool · noun1
lambswool · noun2
Probably identical to Etymology 1, referring to the layer of froth that is produced in making the drink, though starting with Charles Vallancey in 1786, historically supposed to be a corruption of an earlier lamasool or La Maes Abhal "Day of the Apple Fruit" (corresponding to Irish lá measa abhla).
Etymology from Wiktionary, CC BY-SA 4.0.