The comparative ending -er is

The comparative ending -er is a suffix used in English to form the comparative degree of adjectives, indicating that one thing has more of a particular quality than another. For example, "tall" becomes "taller," comparing the height of two subjects. This comparative form is typically used for one-syllable adjectives, though some two-syllable adjectives ending in -y can also take -er, like "happy" becoming "happier."