1. Concrete words--words that have the capacity to stimulate images of one of the five senses
examples: names of colors (red, green, white, etc.)

2. Polysymbolic words--words that have the capacity to stimulate images of more than one of the five senses simultaneously
examples: firey (instead of "red"), celery (instead of "green"), snowy (instead of "white")

3. Emotionally impacted words--concrete or polysymbolic words that have the capacity to stimulate emotional reactions based upon past experiences
examples: casket, watermelon, baseball bat, car accident

4. Figures of Speech--words that make imaginative comparisons
examples of some figures of speech: 
simile: an indirect comparison using "like" or "as"
metaphor: a direct comparison
personification: a comparison with animate subjects
anthropomorphism: a comparison with human attributes
synecdoche: using a part to refer to the whole

(Note:  For these concepts, I am grateful to the late Dr. George O. Williams of Rice University and his book Creative Writing, now out of print.)