They can be both.
Knowledgeable = able as a suffix
I am able to speak. = able as a verb.
Root words, prefixes, and suffixes are the elements used to form medical words. Prefixes are added to the beginning of a root word, and suffixes are added to the end. These elements can modify the meaning of the root word to create specific medical terms.
Root words are parts of words that the structure is based off of. Suffixes come after the root word. Both of these have meaning from the Greek and Latin language.
see
tear duct
care = root word less = suffix
Some words don't have prefixes or suffixes, those words are called root words. Sign, is a root word.
Prefixes; suffixes
come at the end and modify the meaning of the word root.
The core or foundation of a words meaning is the root. Root words can be paired with many different prefixes or suffixes and still maintain the same meaning.
Words with a prefix on the root word man are human and woman. Words with suffixes on the root word man are manhood, and man-cave. Other words with the root "man" include humanity, and womanhood.
englishforstudents.com under etymology
The suffix in carelessness is -ness. This suffix means the state of.