Synonyms of the word

whimsical

• adj. Given to whimsy; capricious; odd; peculiar; playful; light-hearted or amusing.

arbitrary

• adj. (usually of a decision) Based on individual discretion or judgment; not based on any objective distinction,…
• adj. Determined by impulse rather than reason; heavy-handed.
• adj. (mathematics) Any, out of all that are possible.
• adj. Determined by independent arbiter.
• adj. (linguistics) Not representative or symbolic; not iconic.
• n. Anything arbitrary, such as an arithmetical value or a fee.

capricious

• adj. Impulsive and unpredictable; determined by chance, impulse, or whim.

impulsive

• adj. Having the power of driving or impelling; giving an impulse; moving; impellent.
• adj. Actuated by impulse or by transient feelings; inclined to make rapid decisions without due consideration.
• adj. (mechanics) Acting momentarily, or by impulse; not continuous – said of forces.
• n. That which impels or gives an impulse; an impelling agent.
• n. One whose behaviour or personality is characterized by being impulsive.