Easton's Bible Dictionary
Connected with a throne (2 Chronicles 9:18). Jehovah symbolically dwelt in the holy place between the cherubim above the ark of the covenant. The ark was his footstool (1 Chronicles 28:2; Psalm 99:5; 132:7). And as heaven is God's throne, so the earth is his footstool (Psalm 110:1; Isaiah 66:1; Matthew 5:35).
Noah Webster's New International Dictionary of the English Language
(n.) A low stool to support the feet of one when sitting.