Our English word ‘Hypocrite’ comes from the Greek word upokrites [pronounced hoop-o-cree-tays].
In its ancient usage, this word was used to describe the ‘play-actors’ or ‘pretenders’ of the Greek Theater who (obviously enough) wore a mask in order to appear as someone they were not.
Jesus forever changed the definition of this word by applying it to those who wore a mask of piety on the outside, but who were actually haters of God on the inside.
For further study see: Matthew 6:5, 6:16, 7:5, 15:7, 16:13, 22:18, 23:13ff; Luke 13:15, etc.