perfect

(noun): (grammar) The perfect tense, or a form in that tense.
(noun): A perfect score; the achievement of finishing a stage or task with no mistakes.
(adjective): Fitting its definition precisely.
(adjective): Having all of its parts in harmony with a common purpose.
(adjective): Without fault or mistake; thoroughly skilled or talented.
(adjective): Excellent and delightful in all respects.
(adjective): Of a number: equal to the sum of its proper divisors.
(adjective): (grammar, of a tense or verb form) Representing a completed action.
(adjective): Sexually mature and fully differentiated.
(adjective): Of flowers, having both male parts (stamens) and female parts (carpels).
(adjective): Of a set: equal to its set of limit points, i.e. set A is perfect if A=A'.
(adjective): Describing an interval or any compound interval of a unison, octave, or fourths and fifths that are not tritones.
(adjective): (of a cocktail) Made with equal parts of sweet and dry vermouth.
(adjective): Well informed; certain; sure.
(adjective): Innocent, guiltless.

a perfect circle
That bucket with the hole in the bottom is a poor bucket, but it is perfect for watering plants.
Practice makes perfect.
a perfect day
6 is perfect because the sum of its proper divisors, 1, 2, and 3, which is 6, is equal to the number itself.