Adjectives describe nouns. For example: "The timid rabbit hid under the bush."
If you're looking for a verb related to timidity, you might consider words like:
* Hesitate: to pause before doing something because of fear or uncertainty.
* Cower: to shrink back in fear.
* Flinch: to make a sudden, involuntary movement in response to something startling.
* Tremble: to shake involuntarily, usually because of fear or cold.