a particular kind or species of matter with uniform properties(noun.tops)
Example: Shigella is one of the most toxic substances known to man.
source: wordnet30
That which underlies all outward manifestations; substratum; the permanent subject or cause of phenomena, whether material or spiritual; that in which properties inhere; that which is real, in distinction from that which is apparent; the abiding part of any existence, in distinction from any accident; that which constitutes anything what it is; real or existing essence.(noun)
source: webster1913
verb (v)
To furnish or endow with substance; to supply property to; to make rich.(verb)