opportunistic adj.

1881, from opportunism (q.v.) + -ist. A word in Italian politics, later in France opportuniste was applied derisively to the moderate Léon Gambetta (1876), leader of the party between the monarchists and the extreme republicans. In English the word was used generally of anyone whose policy or tendency is to  seek to profit from the prevailing circumstances or take advantage of opportunities as they occur.

Once seated in the legislature Gambetta argued that all republicans—the old guard, young republicans, and even recent converts—could and should cooperate. He preached compromise and accommodation—Opportunism—in order to achieve the politically possible. He spoke against violent revolution and sought to promote peaceful reforms using legal methods, a stance that pitted him directly against the militant demagogue Henri Rochefort, who latched onto the term Opportunism as a term of abuse. [Robert Lynn Fuller, "The Origins of the French Nationalist Movement, 1886-1914"]

Middle English -ik, -ick, word-forming element making adjectives, "having to do with, having the nature of, being, made of, caused by, similar to," from French -ique and directly from Latin -icus or from cognate Greek -ikos "in the manner of; pertaining to." From PIE adjective suffix *-(i)ko, which also yielded Slavic -isku, adjectival suffix indicating origin, the source of the -sky (Russian -skii) in many surnames. In chemistry, indicating a higher valence than names in -ous (first in benzoic, 1791).

In Middle English and after often spelled -ick, -ike, -ique. Variant forms in -ick (critick, ethick) were common in early Modern English and survived in English dictionaries into early 19c. This spelling was supported by Johnson but opposed by Webster, who prevailed.