Full Idea
A relation is 'Euclidean' if aRb and aRc imply bRc.
Gist of Idea
A relation is 'Euclidean' if aRb and aRc imply bRc
Source
Max J. Cresswell (Modal Logic [2001], 7.1.2)
Book Reference
'Blackwell Guide to Philosophical Logic', ed/tr. Goble,Lou [Blackwell 2001], p.141
A Reaction
If a thing has a relation to two separate things, then those two things will also have that relation between them. If I am in the same family as Jim and as Jill, then Jim and Jill are in the same family.