Greek and Latin words for numbers

Prefixes deriving from the Greek and Latin words for numbers form part of many English words, in particular, words for units of measurement (e.g., milligram, centimetre) and for geometrical figures (e.g., hexagon, octahedron).

The following table shows the Greek and Latin words for the cardinal and ordinal numbers from 1 to 12, and for a few larger numbers (20, 100, and 1,000). A cardinal number expresses quantity - so one, two, and three are cardinal numbers - while an ordinal number expresses order - so first, second, and third, are ordinal numbers. (The word 'cardinal' means 'principal, chief, or most important': it derives from the Latin word cardo, which means 'a hinge, i.e., that on which something else depends'. The cardinal numbers are the numbers on which all other types of number (e.g., ordinal numbers, fractions) depend.)

English cardinal number	English ordinal number	Greek cardinal number	Greek ordinal number	Latin cardinal number	Latin ordinal number
one	first	heis (fem. mia, neut. hen)	protos	unus	primus
two	second	duo	deuteros	duo	secundus
three	third	treis	tritos	tres	tertius
four	fourth	tettares	tetartos	quattuor	quartus
five	fifth	pente	pemptos	quinque	quintus
six	sixth	hex	hektos	sex	sextus
seven	seventh	hepta	hebdomos	septem	septimus
eight	eighth	okto	ogdoos	octo	octavus
nine	ninth	ennea	enatos	novem	nonus
ten	tenth	deka	dekatos	decem	decimus
eleven	eleventh	hendeka	hendekatos	undecim	undecimus
twelve	twelfth	dodeka	dodekatos	duodecim	duodecimus
twenty	twentieth	eikosi	-	viginti	vicesimus
hundred	hundredth	hekaton	-	centum	centesimus
thousand	thousandth	chilioi	-	mille	millesimus

For more see Greek or Latin numerical prefix?, Prefixes in units of measurement, Prefixes for very high numbers, and Prefixes in words for geometrical figures.