Why do you Catholics believe in Purgatory when the word "purgatory" isn't even the Bible?

God is perfect holiness: Is 6:3: "let yourselves be built into a spiritual house, to be a holy priesthood, to offer spiritual sacrifices acceptable to God through Jesus Christ." We are called to that same holiness: Mt 5:48: "So be perfect, just as your heavenly Father is perfect." 1 Pet 1:15-16: "...as he who called you is holy; be holy yourselves in every aspect of your conduct, for it is written, 'Be holy because I am holy.'" Without perfect holiness, we cannot see God in heaven. Heb 12:14: "Strive for peace with everyone, and for that holiness without which no one will see the Lord." Rev 21:27: "...nothing unclean will enter it [heaven]." What happens to the faithful who die without perfect holiness or with sin that is not deadly? The biblical, logical, and historical answer is Purgatory. Purgatory comes from the verb "purge" meaning "to purify or cleanse." We should keep this notion of purification in mind when explaining this doctrine.