diffident (adj.)

• bashful
• boggling
• cautious
• cowardly
• coy
• demure
• deprecative
• deprecatory
• faltering
• fearful
• fearing
• fearsome
• goosy
• hesitant
• hesitating
• jumpy
• modest
• mousy
• nervous
• reluctant
• retiring
• scary
• scrupulous
• self-deprecating
• self-effacing
• shaky
• shivery
• shrinking
• shy
• skittish
• squeamish
• sticking
• straining
• tentative
• timid
• timorous
• trembling
• tremulous
• trigger-happy
• unassertive
• unassured