what does the word "blaspheme" literally means ?

Borrowed from Old French blasfemie, from Ecclesiastical Latin blasphēmia, from Ancient Greek βλασφημία (blasphēmía, “profanity”), from βλασφημέω (blasphēméō, “to slander”)

It is a fake crime against a fake character, for which men of ill intent seek retribution.
Remember, if you offend this fake god, men may come to do you harm, and those men decide if it was offended or not.
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I see one christian defining it as anything that is true.  That seems about accurate.

I guess doing a bit of searching online would be too hard.

blas·pheme
verb
- speak irreverently about God or sacred things.

Blasphemy is defamatory, injurious, or abusive speech. Since the holy spirit has God as its Source, saying things against his spirit is the same as speaking against God.

Unrepentantly resorting to speech of that kind is unforgivable.

To answer your question it means The Greek term basically means injurious, defamatory, or abusive speech and was used with reference to such speech whether directed against God or against humans.The English word “blasphemy,” however, is usually restricted to irreverent or abusive speech against God and sacred things. It is thus the antithesis of words of worship directed to the Divine Being. Blasphemy includes the act of claiming the attributes or prerogatives of God, or ascribing these to another person or thing. (Compare Ac 12:21, 22.) The Jewish religious leaders accused Christ Jesus of blasphemy because he said that the sins of certain persons were forgiven (Mt 9:2, 3; Mr 2:5-7; Lu 5:20, 21), and they tried to stone him as a blasphemer because of his declaring himself to be God’s Son. (Joh 10:33-36) When Jesus made a statement to the Sanhedrin concerning God’s purpose toward him and the high position to be granted him, the high priest ripped his garments and accused Jesus of blasphemy, for which Jesus was condemned as worthy of death. (Mt 26:63-66; Mr 14:61-64. Please feel free to read the scriptures that are quoted to get more understaning.

These things:
https://www.dictionary.com/browse/blaspheme

MEAN, not means............

Based on its use in the Holy Bible, the term “blasphemy” is the anglicized form of the Greek word bla·sphe·miʹa. The Greek term basically means injurious, defamatory, or abusive speech and was used with reference to such speech whether directed against God or against humans. (Compare Re 16:11; Mt 27:39.) The English word “blasphemy,” however, is usually restricted to irreverent or abusive speech against God and sacred things. It is thus the antithesis of words of worship directed to the Divine Being.

Further study also teaches us that God does not tolerate blasphemy and should thus is not tolerated by worshipers of God.

Hope that helps!

Charles Darwin's false theory of evolution is a prime example of the definition of blasphemy. 

Blaspheme, according to New World Dictionary of American English, is defined as: "to speak irreverently or profanely of or to God; to curse or revile." Jesus told his followers at Mark 3:28+29: "Truly I say to you that all things will be forgiven the sons of men, no matter what sins they commit and what blasphemes they speak. But whoever blasphemes against the holy spirit has no forgiveness forever but is guilty of everlasting sin." I now invite you to learn more about what the Bible teaches from the international website, jw.org and Bible Teachings > Online Lessons. Thank you for this question.