Egeria was a rather obscure Roman water nymph who was the 'patroness' of Diana's grove at Aricia. Her name means 'black poplar' (aigeiros), and doubtless these were the predominant trees in the grove. Persephone also had a grove of black poplars, trees associated with death.

However, since she was a Roman goddess (or nymph) perhaps we should be looking for a Latin source for her name, and we could consider egero, 'to carry away' - perhaps as a kind of optimistic opposite of infero, 'to bring in' (suggesting something lower or inferior or even infernal).