Digitus : hand ::

A.

genu : leg

B.

manus : finger

C.

dextra : right hand

D.

manus : manacle

E.

genu : foot

Digitus in latin is the same as in English: it means digit.

The relationship between the two words is that the first is a part of the second.

The equivalent relationship is found in A) : Genu means knee, so a knee is a part of the second word, the leg.