the eleventh letter of the alphabet

Cambodia (international vehicle registration)

kelvin(s)

kilobyte(s)

it uses only 10K of RAM

kilometre(s)

a 10K fun run

OK

K, I'm back

kindergarten

school districts may hire uncertified pre-K teachers

king (used especially in describing play in card games and recording moves in chess)

declarer overruffed with ♦K and led another spade

18.Ke2

knit (as an instruction in knitting patterns)

K 42 rows

Köchel (catalogue of Mozart's works)

the Sinfonia Concertante, K364

thousand (used chiefly in expressing salaries or other sums of money)

he earns about £50K a year

the chemical element potassium

(in units of measurement) kilo-

a distance of 700 kpc

a constant in a formula or equation

Boltzmann's constant

the SI base unit of thermodynamic temperature (equivalent in size to the degree Celsius), first introduced as the unit used in the Kelvin scale

the chemical element of atomic number 19, a soft silvery-white reactive metal of the alkali metal group

the ratio of the gas constant to Avogadro's constant, equal to 1.381 × 10?²³ joules per kelvin in the case where the number of molecules is equal to Avogadro's number