Webster's Revised Unabridged Dictionary · 1913

day lily

day lily (lil`y)

(a)
(Botany) any plant of a genus of plants (Hemerocallis) closely resembling true lilies, but having tuberous rootstocks instead of bulbs. The common species have long narrow leaves and either yellow or tawny-orange flowers, which often bloom for only one day.
(b)
(Botany) A genus of plants (Funkia) differing from the last in having ovate veiny leaves, and large white or blue flowers.

Also: daylily