plantain lily, day lily(noun)

any of numerous perennials having mounds of sumptuous broad ribbed leaves and clusters of white, blue, or lilac flowers; used as ground cover

day lily, daylily(noun)

any of numerous perennials having tuberous roots and long narrow bladelike leaves and usually yellow lily-like flowers that bloom for only a day

Day lily(u)

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

Day lily(u)

a genus of plants (Funkia) differing from the last in having ovate veiny leaves, and large white or blue flowers