Stratagem and strategy are sometimes interchangeable, but they are usually not synonyms. The more common strategy is broader. Its main definitions are (1) a plan of action intended to accomplish a specific goal, and (2) the art or skill of using plans or stratagems, especially in war. Stratagem is sometimes synonymous with strategy in military contexts, but its primary definition is a clever scheme for achieving an objective, often by deceiving an enemy. So while strategy can denote any plan of action, stratagem usually implies subterfuge or unconventional tactics.
Both words go back to the Greek strategos, meaning general (the high-ranking military official, not the adjective), but stratagem came directly from the Old French stratageme, and strategy is a newer (19th-century) adaptation of the ancient word. Note that stratagem is spelled with two a‘s rather than two e‘s. The misspelling strategem is common.
Gates’s fight was to buy more time in Washington for the president’s and Petraeus’s war strategy to show results. [Washington Post]
The Stars’ recruitment strategy, according to coach Greg Shipperd yesterday, is to ”get things right on and off the field”. [The Age]
Reinvesting dividends is the best strategy for anyone to grow their wealth. [Telegraph]
By suddenly trying to present his sexting scandal as a medical matter in yet one more stratagem to save his job, Weiner has veered off into a publicity wasteland. [Toronto Star]
But the stratagem of playing the Republican Legislature as a foil seems to have been shelved when Eileen Klein was elevated to chief of staff. [AZ Central]
The more cynical of the political analysts point out that this is a stratagem to weaken the power base of the PML-N. [The Express Tribune]