Baptisms is the Greek word βαπτισμος and that is plural.

Hebrews 6:1-2 - Therefore, leaving the discussion of the elementary principles of Christ, let us go on to perfection, not laying again the foundation of repentance from dead works and of faith toward God, of the doctrine of baptisms, of laying on of hands, of resurrection of the dead, and of eternal judgment.

There are 7 Baptisms in Scripture:

1. John's baptism in water
Luke 7:29-30 - And when all the people heard Him, even the tax collectors justified God, having been baptized with the baptism of John. But the Pharisees and lawyers rejected the will of God for themselves, not having been baptized by him.

2. Christ's baptism in water
Matthew 3:13 - Then Jesus came from Galilee to John at the Jordan to be baptized by him.

3. Baptism in suffering
Luke 12:50 (Amplified Bible) - I have a baptism [of great suffering] with which to be baptized, and how [greatly] I am distressed until it is accomplished!

4. Baptism in the cloud and in the sea
1 Corinthians 10:2 - all were baptized into Moses in the cloud and in the sea,

5. Baptism into Christ and into His body
Romans 6:3 - Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death?

6. Christian baptism in water
Matthew 28:19 - Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,

7. Baptism in the Holy Spirit
Acts 1:8 - But you shall receive power when the Holy Spirit has come upon you; and you shall be [witnesses to Me in Jerusalem, and in all Judea and Samaria, and to the end of the earth."