Aquitard

Geological formation that may contain groundwater but is not capable of transmitting significant quantities of it under normal hydraulic gradients. May function as confining bed.
Found on http://www.epa.gov/OCEPAterms/

Aquitard

A geological formation that prevents significant flow of water (e.g. clay).
Found on http://www.encyclo.co.uk/visitor-contributions.php

aquitard

aquitard 1. A leaky confining bed that transmits water at a very slow rate to or from an adjacent aquifer. 2. A bed of low permeability adjacent to an aquifer. An aquitard may serve as a storage unit for groundwater, although it does not yield water readily.
Found on http://www.wordinfo.info/words/index/info/view_unit/3692/

aquitard

A layer of rock having low permeability that stores groundwater but delays its flow.
Found on http://www.inlandlapidary.com/user_area/glossaryA.asp

aquitard

A material of low permeability that greatly slows the movement of ground water.
Found on http://www.ge-at.iastate.edu/glossary-of-geologic-terms/

Aquitard

A geologic formation or stratum that significantly retards fluid movement.
Found on http://jersey.uoregon.edu/~mstrick/geology/geo_glossary_page.html

Aquitard

A rock with limited permeability that allows some water to pass through it, but at a very reduced rate.
Found on http://www.bgs.ac.uk/discoveringGeology/glossary.html
No exact match found