This is a grid of all of the New Testament occurrences of the Greek root word βαπτ, bapt, which is the root of such words as baptize, baptized, baptism, etc.  When you hover over a verse on the left, the Bible text that pops up is from the New American Standard Bible.

In Greek nouns decline; that is, they change form.  We really don’t have an equivalent in English except for such words as actor, actors, actress, actresses.  The “act” is the root and the noun “declines.”  It changes form depending on usage.  This is the same for Greek, except that every noun does this for masculine, feminine, neuter, singular, plural, nominative case (subject), genitive case (possession), dative case (indirect object), and accusative case (direct object).  Therefore, we can have Greek words such as baptisthato, baptisai, baptisma, baptismois, etc.

Many people assume that baptism always means immerse.  It does not.  Take a look at these verses where bapt is translated differently:  Mark 7:4 (cleans and washing); Mark 10:38 (baptism of tribulation); Luke 12:50 (baptism of tribulation); Heb. 6:2 (washings); Heb. 9:10 (washings).