Quiescent: motionless, still, at rest
Example: [relatively quiescent]

Quiet: Making no noise.

Quietude: tranquility
Example: [the monk lived in quietude of the jungle]

Quietus: eternal sleep, death, final discharge, termination, final settlement (as of a debt or obligation)
Example: [Before he is well awake here, he arrives at the world below, and has his final quietus]

Quintessence: The most essential part of anything

Quintet: Musical composition arranged for five voices or instruments.

Quip: joke
Example: [who made the famous quip about life mimicking art]

Quirk: eccentricity
Example: [By an odd quirk of fate]

Quite: Fully.

Quiver: shake, spasm, shiver, tremor, tremble
Example: [a quiver in his voice]

Quixotic: romantic impractical
Example: [This is a vast, exciting and some say quixotic project]

Quizzical: odd
Example: [a quizzical look]

Quorum: majority
Example: [for certain decision, a quorum has to be present]

Quota: a share or proportion
Example: [the usual quota]