What suffix do all but one word have in common?

A suffix is a group of letters placed at the end of a word to make a newword. A suffix can make a new word in one of two ways:

1. Infectional: For Example, changing singular to plural (dog ➡dogs), or changing present tense to past tense (walk ➡walked). In this case, the basic meaning of the word does not change.

2. Derivational (the new word has a new meaning "derived" from the original word) : for example, teach➡teacher or care➡careful