Either of two plants with deep purple flowers, both native to Europe and cultivated elsewhere: (a) dusky cranesbill, Geranium phaeum, of central Europe.
Origin
Early 19th century (in an earlier sense). From mourning + widow.
Definition of mourning widow in US English:
mourning widow
nounˌmɔːnɪŋ ˈwɪdəʊ
Either of two plants with deep purple flowers, both native to Europe and cultivated elsewhere: (a) dusky cranesbill, Geranium phaeum, of central Europe.
Origin
Early 19th century (in an earlier sense). From mourning + widow.