Either of two composite plants with blue flowers somewhat resembling those of the dandelion, chicory, Cichorium intybus, and a wild lettuce, Lactuca sonchifolia, which also has toothed dandelion-like leaves.
Origin
Mid 19th century.
Definition of blue dandelion in US English:
blue dandelion
noun
rare
Either of two composite plants with blue flowers somewhat resembling those of the dandelion, chicory, Cichorium intybus, and a wild lettuce, Lactuca sonchifolia, which also has toothed dandelion-like leaves.