1. underdrag - Noun
2. underdrag - Verb
underdrag (usually uncountable, plural underdrags)
(geology) The tensile stress exerted by an overthrust rock mass upon overlying rocks which themselves are not under compressive thrusting stress and therefore tend to be stretched and broken by normal faulting.
(transitive) To exert pull on the underside of (something).
(intransitive) To undergo a pull from the underside.
Source: en.wiktionary.org