From Popes to realpolitiks
Any person that takes advantage of circumstances without regard to what is just or honest can be described as an opportunist. The term is derived from the French opportuniste and first appeared in the English language during the 19th century. The root word is Latin opportunus from around 1408 the phrase ob portum veniens meaning "coming toward a port." This is a reference to the wind, from ob which indicates to or toward and portus meaning harbor. Both opportunism and opportunist were eventually borrowed from Italian politics opportunismo. In the Roman Catholic Chrurch during the Vatican Council of 1870 an opportunist was a person who held that "the time was opportune for the promulgation of the doctrine of Papal Infallibility." By 1881 Opportunist was used to denote a political party in France. In particular it was used frequently to refer to French republican statesman Léon Gambetta (1838-82).
In 1902 the word reappeared in the German political realm indicating 'proponents or practitioners of opportunism to portray any socialist or communist who advocates the making of concessions to the bourgeoisie.' Eventually the term crept into the English language to describe anyone who "seeks profit from the prevailing circumstances."
Carpetbaggers and making hay while the sunshines
Biological organisms are called opportunist as well. For example some medical professionals theorize that pulmonary disease is caused by opportunist mycobacteria. The opportunists of the plant world are primary grasses. These emerge soon after a forest fire and stabilize the freshly bared ground until the more prevalent species of larger plants like trees arrive as replacements. The alder is primarily a pioneering arboreal and considered as opportunist species by ecologists because of its capacity for direct colonization of even the rawest soil material. The spotted hyena (Crocuta crocuta) are known to be opportunists in the animal kingdom because their foraging habits. Even though they are primarily hunters that have a varied diet including mammals, reptiles and birds, they will scavenge wherever and whenever possible.
Allwords.com Definition of opportunist