Nec vi, nec clam, nec precario, is a Latin legal term meaning 'without force, without secrecy, without permission'. It is the principle by which rights may be built up over time, principally public rights of way in the United Kingdom. Specifically, if a path is used – openly, not against protests, and without permission of the landowner – for an extended period (20 years) then a permanent legal right to such use is usually established.
It is often referred to in the context of adverse possession and other land law issues. It is also relevant to the creation of easements whereby the law 'prescribes' an easement in the absence of a deed. In order for the law to do so the right of way or easement needs to have been enjoyed without force, without secrecy, and without permission for a period of time, usually 20 years.