downhole

adj, noun

adj

Etymology From down- + hole.

Located in the drilled bore of an oil well either underground or undersea.

In the work over, part of the new "string" was a down-hole titanium gauge.2005, Paul Carter, Don't Tell Mum I Work on the Rigs, Crows Nest: Allen and Unwin, page 44:
Pressure readings are taken downhole next to the feed zone and the total flow is measured on the surface using a separator.2015, Ronald DiPippo, Geothermal Power Plants:

noun

Etymology From down- + hole.

Entry derived from the Wiktionary, under licence CC BY-SA 4.0 — list of authors.