PERCENT
percentage, percent, per centum, pct
(noun) a proportion in relation to a whole (which is usually the amount per hundred)
Source: WordNet® 3.1
Etymology
Adverb
percent (not comparable)
For every hundred (used with preceding numeral to form a noun phrase expressing a proportion). [from 16th c.]
Usage notes
• A percentage is often denoted by the character %.
• The difference of two percentages is measured by percentage point, not by percent.
Noun
percent (plural percent or percents)
A percentage, a proportion (especially per hundred).
One part per hundred; one percent. [from 19th c.]
Prepositional phrase
percent
Per hundred.
Usage notes
• Percent/per cent originated as a shortening of the Latin phrase per centum, “per hundred”, and historically the use of the word as a noun (as in “half a percent” or “percents”) was regarded as an error, though such use has now become so common that it is recognized by all other major dictionaries, and a few treat the word as being only a noun. Of those which recognize non-nounal uses, most label it an adverb and many also label it an adjective though it does not meet tests of adjectivity.
Source: Wiktionary