These words are applied to actions or persons characterized by a lack of forethought, warning or preparation. Impetuous and impulsive differ from the other words in applying to both people and actions. Impetuous suggests more decisive or vigorous action than impulsive , and often implies an unfortunate outcome as a result. Impulsive means acting on impulse, and since impulses can be good as well as bad, impulsiveness is not necessarily deplorable; it may even be considered endearing or attractive. Impetuosity , on the other hand, implies a rather childish inability to be patient or thoughtful before taking action.

• Hers was a generous, impulsive nature, capable of showing spontaneous affection and warmth; an impetuous decision that he later learned to regret; to stamp his foot in an impetuous rage.

Impulsive need not always imply recklessness, and in some contexts may only imply spontaneity and the lack of premeditation: an impulsive urge to re-open the door and check to see if all the windows were closed before she left for the weekend.

Headlong suggests a reckless disregard of consequences coupled with impetuous haste. Unlike the other words here considered, headlong is used as both an adjective and an adverb; it is somewhat more formal when used as an adjective: a headlong advance into enemy territory; women rushing headlong into the store at the start of the sale; to plunge headlong into a new business without adequate financial backing. Where headlong points to a complete lack of deliberation, precipitate suggests that what deliberation did occur was grossly inadequate to prepare for the ensuing action; a precipitate action is therefore premature and rash.

• The editorial called the union’s rejection of management’s wage offer precipitate and unwarranted.

Sudden , as here considered, suggests an abrupt or unexpected action but does not necessarily imply haste; it does point to either a spontaneous, unpremeditated act or a perception for which one is not prepared.

• A sudden rush for the door when someone shouted, "Fire!"; his sudden departure from the published text of the speech caught us all by surprise; The sudden stop of the crowded bus threw several people to the floor.