The scriptures have defined faith in Hebrews 11:1 which says. Now faith is the substance of things hoped for, the evidence of things not seen.

This means for somebody to have faith he or she must have hope, then by the eyes of the spirit he or she sees it as a reality and becomes fully persuaded.

I found another definition of faith in Luke 20:1-6.

This portion of scripture says:

1 And it came to pass, that on one of those days, as he taught the people in the temple, and preached the gospel, the chief priests and the scribes came upon him with the elders, 2 And spake unto him, saying, Tell us, by what authority doest thou these things? or who is he that gave thee this authority?3 And he answered and said unto them, I will also ask you one thing; and answer me:4 The baptism of John, was it from heaven, or of men? 5 And they reasoned with themselves, saying, If we shall say, From heaven; he will say, Why then believed ye him not? 6 But and if we say, Of men; all the people will stone us: for they be persuaded that John was a prophet.

This definition comes from the reasoning of the religious experts in Israel in the above passage. They asked Jesus if His authority was from God or from men.

But, Jesus is too wise for His creatures to challenge Him. When they asked two questions, Jesus also asked them one question.

However, the question which Jesus asked was so enamored with wisdom, that the religious experts knew the answer by themselves. Jesus knew that they had heard John say that Jesus was send from heaven and was authorized by the Almighty to be the anointed one. But probably Jesus could not fit into their definition of the Messiah. So, they decided to confirm the source of Jesus authority. Brethren, the Lord Jesus always takes us to the original plan of God. He took them to the beginning of His ministry. The beginning of His ministry was clearly demonstrated by John to be God ordained. Every body was persuaded that this was God speaking to men. John never did any miracle, but the anointing in his life convinced every one that He who comes after him was mightier that him. See Matthew 3:11. Which says I indeed baptize you with water unto repentance: but he that cometh after me is mightier than I, whose shoes I am not worthy to bear: he shall baptize you with the Holy Ghost, and with fire:

We are supposed to believe the messages from heaven. (Isaiah 53:1). The religious leaders knew this, they reasoned among themselves, and said, if we say, He shall say….if John was a prophet why did they not believe on him?  We are supposed to believe the prophets. 2 Chronicles 20:20 which says, believe his prophets, so shall ye prosper.

Now look at the summary of there Jesus driven reasoning:  If people believe in something they become fully persuaded. They can even stone you if you speak against what they believe. Be careful.  Therefore, if you say you have faith and you can not die for it you have not really believed it. You are to believe it and be able to defend it.

Therefore, to believe means to be fully persuaded about somebody or something.