Definition of Leaven:

1. Leaven is a type of prideful sin.

Definition of Leaven - Define Leaven from Old Testament Scripture

Ex 12:19 Seven days shall there be no leaven found in your houses: for whosoever eateth that which is leavened, even that soul shall be cut off from the congregation of Israel, whether he be a stranger, or born in the land.

(we have only included one Scripture from the Old Testament Scripture, but there are many.  In the old testament, leaven was a part of feasts that pointed to what God intended to do in the New Testament and intends to do when the Feast of Tabernacles is finally fulfilled.)

Definition of Leaven - Define Leaven from New Testament Scripture

Mt 13:33 Another parable spake he to them; The kingdom of heaven is like to leaven, which a woman took, and hid in three measures of meal, till the whole was leavened.
Mt 16:6 Then Jesus said to them, Take heed and beware of the leaven of the Pharisees and of the Sadducees.
Mt 16:11 How is it that ye do not understand that I spake it not to you concerning bread, that ye should beware of the leaven of the Pharisees and of the Sadducees?
Mt 16:12 Then understood they how that he bade them not beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees.
Mr 8:15 And he charged them, saying, Take heed, beware of the leaven of the Pharisees, and of the leaven of Herod.
Lu 12:1 In the mean time, when there were gathered together an innumerable multitude of people, insomuch that they trode one upon another, he began to say to his disciples first of all, Beware ye of the leaven of the Pharisees, which is hypocrisy.
Lu 13:21 It is like leaven, which a woman took and hid in three measures of meal, till the whole was leavened.
1Co 5:6 Your glorying is not good. Know ye not that a little leaven leaveneth the whole lump?
1Co 5:7 Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us:
1Co 5:8 Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.
Ga 5:9 A little leaven leaveneth the whole lump.