
1) Chinese invention 2) Mining passage
Found on
https://www.crosswordclues.com/clue/borehole

A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid (such as petroleum) or gases (such as natural gas), as part of a geotechnical investigation, environmental site assessment, mineral exploration, temperatur...
Found on
http://en.wikipedia.org/wiki/Borehole

Any deep or long drill-hole, usually associated with a diamond drill.
Found on
http://www.australian-shares.com/glossary-of-terms.php.html

(from the article `exploration`) Direct sampling, generally by means of boreholes, is often required to make positive identification of substances and to determine the quantity, as ... ...of the Earth, however, can be studied in this way. Investigators can drill into only the uppermost crust, and the high cost severely limits the ... ...
Found on
http://www.britannica.com/eb/a-z/b/94

Any deep or long drill-hole, usually associated with a diamond drill.
Found on
http://www.coaleducation.org/glossary.htm

Any exploratory hole drilled into the Earth or ice to gather geophysical data. Climate researchers often take ice core samples, a type of borehole, to predict atmospheric composition in earlier years. See ice core
Found on
http://www.encyclo.co.uk/visitor-contributions.php

Hole made with drilling equipment.
Found on
http://www.encyclo.co.uk/visitor-contributions.php

a hole made by drilling or boring; a wellbore.
Found on
http://www.encyclo.co.uk/visitor-contributions.php

The hole that is made from drilling a well, core etc.
Found on
http://www.juniorminers.com/glossary.html

The hole as drilled by the drill bit.
Found on
http://www.oilandgasuk.co.uk/glossary.cfm

Any deep or long drill-hole, usually associated with a diamond drill.
Found on
http://www.rocksandminerals.com/glossary.htm

Hole made with drilling equipment.
Found on
https://www.encyclo.co.uk/local/20094

The circular hole made by drilling that extends from the surface to the gas resource to be recovered.
Found on
https://www.encyclo.co.uk/local/22831

a hole drilled in the earth, as for the purpose of extracting a core, releasing gas, oil, water, etc.
Found on
https://www.infoplease.com/dictionary/borehole
No exact match found.