three syllables with third stressed: a metrical foot of three syllables with the stress on the third syllable, or of two short syllables followed by a long syllable. The word "unconcerned" and the phrase "up the hill" are anapests.
[Late 16th century. Via Latin< Greek anapaistos "struck backward" (from its being a reversed dactyl), past participle of anapaiein< paiein "strike"]