Where does “δέον” come from?

δέον (Ancient Greek) comes from Ancient Greek δεῖ, from Ancient Greek δέω, from Proto-Indo-European deh₁- — to bind.

δέον (Ancient Greek): nominative/accusative/vocative singular neuter of...

Definitions

Step	Language	Word	Meaning
1	Ancient Greek	δεῖ	it behoves one to, it is necessary to, one must;...
2	Ancient Greek	δέω	I bind, tie, fasten, fetter; To lack, need,...
3	Proto-Indo-European	deh₁-	to bind