To irritate someone is to excite them to impatience or anger. This verb is commonly used to talk about an emotional disturbance that is relatively short-lived and not terribly deep—it might irritate you, for instance, if someone refuses to answer a question. The synonym rankle implies continued anger or emotional disturbance. When something rankles you, it causes keen irritation or bitter resentment, the kind that builds over time or festers. Harsh criticism from a colleague might rankle you, or eat at you, long after it is uttered. Unpleasant though all of this may be, the term's meaning has softened over time; on entering English, rankle referred to the festering or putrefaction of physical wounds.

On this day in 1776, the Continental Congress adopted the Declaration of Independence, which announced the colonies as "Free and Independent States." Independent, in this historical context, means "not subject to another's authority or jurisdiction." But the adjective has many applications that do not deal with matters of government or political rule: an independent thinker, for instance, is someone who is not influenced or controlled by others in matters of opinion. The synonym autonomous is commonly used to describe self-governance, especially in the context of regions that have power over their own affairs, as certain parts of China. Though you may encounter this freewheeling descriptor used of vehicles that are able to operate with little or no human control or intervention.

We say something is risky when it involves the chance of loss or injury (a risky chess move, a risky investment). Perilous suggests a much higher degree of danger. Something is perilous if it is full of grave risk or imminent danger or destruction (a perilous ocean voyage in a small boat). Generally, risky applies to actions: a person’s risky activities or behavior expose them to hazards. Perilous usually applies to positions or situations someone is in, rather than particular actions they take, and perilous situations are often extended undertakings one has to get through—a perilous journey, perilous mission, or the perilous fight survived by the Star-Spangled Banner during the Battle of Baltimore.  That said, life doesn’t have to be at stake for something to be perilous. Perilousness can be political, economic, spiritual, or emotional in nature.