large or extensive in breadth or importance or comprehensiveness; "the might have repercussions of unimaginable largeness"; "the very extensiveness of his power was a temptation to abuse it"
a device for showing the operating condition of some system
a signal for attracting attention
(chemistry) a substance that changes color to indicate the presence of some ion or substance; can be used to indicate the completion of a chemical reaction or (in medicine) to test for a particular reaction