Definition of "capaciously"

But my Leech—a leechFit to suck blood, with lubricous round rings,Capaciously expatiative, which makeHis little body like a red balloon,As full of blood as that of hydrogene,Sucked from men’s hearts

1820, Percy Bysshe Shelley, Oedipus Tyrannus; Or, Swellfoot The Tyrant: A Tragedy in Two Acts