Oblique derives from Latin obliquus, meaning slanting, sideways, or indirect. The word is probably compounded from ob- (against, toward) and a root related to licinus (bent upward), though the exact formation is debated. The sense of going against the straight line — refusing the direct path — is embedded in the word's structure.
The word entered English in the 15th century through Old French and has maintained its core meaning across multiple domains: geometry, rhetoric, anatomy, military science, and everyday speech. An oblique angle is neither right nor straight. An oblique reference is indirect. An oblique muscle runs diagonally. An oblique strategy approaches a problem from an unexpected direction.
In classical rhetoric, oblique speech (oratio obliqua) was indirect discourse — reporting what someone said without quoting them directly. This grammatical sense preserves the Latin understanding of obliquus as indirect: the oblique approach avoids the straight confrontation of direct quotation.
The military oblique order became one of the most celebrated tactical innovations of the 18th century. Frederick the Great of Prussia perfected the technique of advancing his army at an oblique angle to the enemy line, concentrating overwhelming force on one end while holding back (refusing) the other. This allowed him to defeat armies larger than his own at battles like Leuthen (1757), one of the most decisive victories in military history.
In typography, the oblique stroke (/) — also called a solidus, virgule, or slash — takes its name from its slanting orientation. The term oblique is also used to distinguish certain typeface variants from true italics: an oblique typeface simply slants the roman letterforms, while true italics are redesigned letter shapes.
Brian Eno and Peter Schmidt's Oblique Strategies cards, created in 1975, use the word in its most productive metaphorical sense: approaches to creative problems that come at them sideways rather than head-on. The cards contain cryptic suggestions ('Use an unacceptable color,' 'What would your closest friend do?') designed to break creative blocks through indirect, oblique thinking.
The word oblique thus embodies a philosophy as well as a geometry: the idea that the indirect approach is sometimes more effective than the direct one — in war, in art, in argument, and in life.