What does "lambkill" mean?

Any of species Kalmia angustifolia of toxic plants with small, deep pink flowers.

Lambkill

Common synonyms include: butcher, kalmia angustifolia, kill, lamb loss, lamb mortality, neonatal mortality.

noun

noun ·Rare ·Advanced level

Noun

1
Any of species Kalmia angustifolia of toxic plants with small, deep pink flowers. uncountable
2
North American dwarf shrub resembling mountain laurel but having narrower leaves and small red flowers; poisonous to young stock wordnet

From lamb + kill.