Strongs Number: G2219
Orig: probably from 2204; ferment (as if boiling up):--leaven. G2204
Use: TDNT-2:902,302 Noun Feminine
Heb Strong: H2557 H7603
2) metaph. of inveterate mental and moral corruption, viewed in its tendency to infect others
Leaven is applied to that which, though small in quantity, yet by its influence thoroughly pervades a thing; either in a good sense as in the parable Mt 13:33; or in a bad sense, of a pernicious influence, "a little leaven leaveneth the whole lump"