These words refer to easy, timely, fortunate or practical actions that promote self-interest and the hope of gain or advancement. Opportune has the widest range of application. It may suggest chance action that gives unexpectedly good results: an opportune change of plans that placed them far from the area where the disaster occurred; an accidental encounter that proved to be opportune . More commonly the word suggests a conscious choice with an eye to suitability or timing: an opportune moment to oppose the Prime Minister. Often the word suggests action that is taken to ingratiate or advance oneself; a note of insincerity may sometimes be present: making opportune remarks that he knew would flatter the prejudices of his superior.

Advantageous lays its stress on favourable results; these may be arrived at by chance or design, but the word in any case often suggests a self-interested rather than altruistic attitude: happening on the most advantageous spot for viewing the sunset; seeking out the most advantageous positions from which to attack the enemy; driving the most advantageous bargain possible; lobbying for legislation that would be advantageous to his backers. Convenient suggests considerations of ease and comfort: a flat convenient to the city bus route. The word is often used to imply that these considerations have outweighed such ethical concerns as truth or fairness: telling convenient lies, careless of whom she hurt; convenient excuses; convenient compromises that would offend no one but accomplish nothing.

Expedient and politic refer much more strongly to narrow self-interest. Most neutrally, expedient can indicate an improvised or temporary solution taken out of necessity: an expedient repair job that would at least get them to the next town. The conflict between self-interest and ethics is amply apparent in most other uses: appealing to the country’s immigrant population as a purely expedient political gesture; twisting the facts outrageously whenever he thought it expedient . Politic is milder than expedient , suggesting actions governed more by immediate practical considerations than by any larger view: those who think it politic never to disagree with their employers. The word certainly suggests insincerity and the currying of favour, if not the disregard of ethics possible for expedient : another excruciating attempt to be politic about his mother-in-law’s view on current affairs.