cahier n.

Proto-Indo-European root meaning "four."

It forms all or part of: cadre; cahier; carillon; carrefour; catty-cornered; diatessaron; escadrille; farthing; firkin; fortnight; forty; four; fourteen; fourth; quadrant; quadraphonic; quadratic; quadri-; quadrilateral; quadriliteral; quadrille; quadriplegia; quadrivium; quadroon; quadru-; quadruped; quadruple; quadruplicate; quarantine; quarrel (n.2) "square-headed bolt for a crossbow;" quarry (n.2) "open place where rocks are excavated;" quart; quarter; quarterback; quartermaster; quarters; quartet; quarto; quaternary; quatrain; quattrocento; quire (n.1) "set of four folded pages for a book;" squad; square; tessellated; tetra-; tetracycline; tetrad; tetragrammaton; tetrameter; tetrarch; trapezium.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit catvarah, Avestan čathwaro, Persian čatvar, Greek tessares, Latin quattuor, Oscan petora, Old Church Slavonic četyre, Lithuanian keturi, Old Irish cethir, Welsh pedwar.

c. 1200, quaier, "a short book;" mid-15c., "a set of four folded pages for a book; pamphlet consisting of a single quire," original senses now obsolete, from Anglo-French quier, Old French quaier, caier "sheet of paper folded in four" (Modern French cahier), from Medieval Latin quaternum, "set of four sheets of parchment or paper," from Vulgar Latin *quaternus, from Latin quaterni "four each," from quater "four times" (from PIE root *kwetwer- "four").

Meaning "standard unit for selling paper" (lately typically 24 or 25 sheets, the twentieth part of a ream) is recorded from late 14c. In quires (mid-15c.) means "unbound."