English Synonyms and Antonyms, by James Champlin Fernald
To fluctuate (Latin fluctus, a wave) is to move like a wave with alternate rise and fall. A pendulum oscillates; waves fluctuate or undulate; a light or a flame wavers; a frightened steed swerves from his course; a tool or weapon swerves from the mark or line; the temperature varies; the wind veers when it suddenly changes its direction. That which veers may steadily hold the new direction; that which oscillates, fluctuates, undulates, or wavers returns upon its way. As regards mental states, he who hesitates sticks (Latin hærere) on the verge of decision; he who wavers does not stick to a decision; he who vacillates decides now one way, and now another; one vacillates between contrasted decisions or actions; he may waver between decision and indecision, or between action and inaction. Persons hesitate, vacillate, waver; feelings fluctuate or vary. Compare SHAKE.