Suffix -ER is a vowel suffix. Suffix -ER can change the base word meanings in different ways:

Suffix -ER can be used to change a word to “compare between two things”, as in “slow” to “slower”.  It is not used to compare more than two things.

Suffix -ER can also change the word to mean “someone who” or “something that”, as in “walk” to “walker”, which can be a person or something that helps with walking.

Suffix /ər/, Suffix /ər/, Suffix /ər/, slower, walker

When ER occurs at the end of a word, as in “her”, it is not always acting as a suffix. When ER occurs earlier in a word it also says /Ər/, as in “mermaid”, but it is not acting as a suffix. 

This is explored in later lessons.