houseleek
noun
house·leek ˈhau̇s-ˌlēk 
: a pink-flowered thick-leaved European plant (Sempervivum tectorum) of the orpine family that tends to form clusters of rosettes and is often grown in rock gardens
broadly : sempervivum
Word History
Etymology
Middle English houslek, from hous house entry 1 + lek leek
Note: The formation is paralleled by Middle Dutch huuslooc, Middle High German huslouh, Old Danish husløk, and Old Swedish husslök. The name is alleged to have originated from the custom of growing Sempervivum tectorum (the specific epithet meaning "of the roofs") on the roofs of houses to ward off lightning.
First Known Use
14th century, in the meaning defined above