nailbourne
A chalk stream that only flows intermittently.
It should be understood that many small springs were not visited, and that the subject of streams and nailbournes (or occasional streams) has been only alluded to incidentally.
Where it comes from
From nail + bourne (“seasonal stream or brook”). The etymology of the first part is uncertain. It may derive from ail via a rebracketing of an ailbourne as a nailbourne; compare similar cases such as English newt and nickname.
Adapted from the Wiktionary entry nailbourne (CC BY-SA 4.0).