Source : Webster's Revised Unabridged Dictionary (1913)

Circumflex \Cir"cum*flex\, v. t. [imp. & p. p. {Circumflexed};
   p. pr. & vb. n. {Circumflexing}.]
   To mark or pronounce with a circumflex. --Walker.

Circumflex \Cir"cum*flex\, a. [Cf. L. circumflexus, p. p.]
   1. Moving or turning round; circuitous. [R.] --Swift.

   2. (Anat.) Curved circularly; -- applied to several arteries
      of the hip and thigh, to arteries, veins, and a nerve of
      the shoulder, and to other parts.

Circumflex \Cir"cum*flex\, n. [L. circumflexus a bending round,
   fr. circumflectere, circumflexum, to bend or turn about;
   circum + flectere to bend. See {Flexible}.]
   1. A wave of the voice embracing both a rise and fall or a
      fall and a rise on the same a syllable. --Walker.

   2. A character, or accent, denoting in Greek a rise and of
      the voice on the same long syllable, marked thus [~ or ?];
      and in Latin and some other languages, denoting a long and
      contracted syllable, marked [? or ^]. See {Accent}, n., 2.

Source : WordNet®

circumflex
     n : a diacritical mark (^) placed above a vowel in some
         languages to indicate a special phonetic quality