We don't have synonyms for day lily yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are daylily, may lily and day fly.
(n) :
Alternative form of daylily. [Any of several perennial plants, of the genus Hemerocallis, that have fleshy roots, grasslike leaves and colourful flowers that bloom for just one day.]
(n) :
Alternative form of daylily. [Any of several perennial plants, of the genus Hemerocallis, that have fleshy roots, grasslike leaves and colourful flowers that bloom for just one day.]