Shadows have a life of their own. During construction, a shadow (or its poor proxy, the 'Measure-of-a-Man' (see History) is buried beneath a foundation stone to create a foundation shade. These entities protect the building. Unfortunately, a creature or person who loses their shadow (ie. who becomes anumbrate) only has 40 days of life left before they die.
Exumbrate: v. To remove a shadow.
Anumbrate: n. One who has no shadow.
Conumbrum: n. Unofficially, a person with two shadows (Arcturus). As no technique for only partially severing a shadow is known commonly to exist, Arcturus and his patron Samovar jokingly refer to Arcturus's state of being bi-shadowed using this neologism, which is a pun on conundrum and the suffix -umbrate, 'to have a shadow'.
You have 40 days of life without a shadow. You can halt this countdown by nailing a replacement shadow to the soles of your feet using cold iron nails. While the blood flows, the shadow stays attached (The Conumbrum).
If you have no shadow, any child conceived by you has no shadow (and subsequently dies at 40 days after conception) (Womb-Of-Mine).
it is possible to attach your shadow to an inanimate object to convey a brief message (Caesura).