two vs span

two and span both are nouns.

Word	Noun	Adjective	Verb	Adverb
two	Yes	Yes	No	No
span	Yes	No	Yes	No

As nouns, span is a hyponym of two; that is, span is a word with a more specific, narrower meaning than two:

two: the cardinal number that is the sum of one and one or a numeral representing this number
span: two items of the same kind

Other hyponyms of two include craps, snake eyes, brace, couple, couplet, distich, duad, duet, duo, dyad, pair, twain, twosome, yoke.

two (noun)	span (noun)
one of the four playing cards in a deck that have two spots	the act of sitting or standing astride
the cardinal number that is the sum of one and one or a numeral representing this number	a structure that allows people or vehicles to cross an obstacle such as a river or canal or railway etc.
	the distance or interval between two points
	a unit of length based on the width of the expanded human hand (usually taken as 9 inches)
	two items of the same kind
	the complete duration of something

two (adjective)	span (adjective)
being one more than one

two (verb)	span (verb)
	to cover or extend over an area or time period