Wiktionary
joint will
n. (context legal English) A single document executed by two people, so that their property is disposed of identically upon the death of either or both.
Usage examples of "joint will".
As the plant is a perennial, spreading by means of its underground, creeping stems propagation may be easily effected by lifting the roots in February or March, dividing them - every piece showing a joint will grow - and planting again in shallow trenches, covering with 2 inches of soil.