1) Matter 2) Substance 
A gelatinous colloid in unstable equilibrium with its contained water, useful in dentistry for impressions because of its dimensional stability under controlled conditions. ... (05 Mar 2000) ... 
(hi″dro-kol´oid) a colloid in which water is the dispersion medium; one type is used in dentistry as an impression material.
Type: Term Pronunciation: hī′drō-kol′oyd Definitions: 1. A gelatinous colloid in unstable equilibrium with its contained water, useful in dentistry for impressions because of its dimensional stability under controlled conditions.
[n] - a substance that forms a gel with water
hydrocolloid An elastic water-based impression material.
a substance that forms a colloid when combined with water.