Not only is it unusual, it's incorrect. There are other grammatical mistakes on that website.
With this use of adjectives you need to remember that the only acceptable determiner is "the". The adjective "unemployed" normally modifies a noun, but in this case it is fused with the noun head, and we understand "the unemployed" as a fused-head noun phrase, with a plural interpretation.In CGEL they classified this construction as a subclass of the fused-head construction which they named "Modifier-head with special interpretations". "The NPs are determined by the definite article - we couldn't even substitute a demonstrative: *these very poor (instead of "the very poor" in "How will the new system affect the very poor? wouldn't be acceptable) (p417)I've just come across the following definition of "unemployed" in Pearson's online application - "Vocabulary Trainer": "Someone who does not have a job."
It suggests that it is a noun and can be used in the singular, while mostly it is used as an adjective.
It is the first sentence of the third paragraph. At the end of that paragraph there is another sentence with "an unemployed": "An unemployed should check their contract to see any variations.""An unemployed" must be followed by a noun (e.g. person, actor).
I can't find the sentence Usually an unemployed ... in the source you quote.
This is another example of non-native English - cf. the mistake in the emboldened section. When adjectives are used to describe a group, they cannot refer to individuals.Another example from the Net:
"The longer an unemployed is without work, the lower chances he/she has for finding a job."
Source: "High unemployment rate in the USA." Website: worldpoliticsjournal.com.
In the list of authors there is only one English name:
C. S. Kuppuswamy
Your example shows the word "unemployed" can be used without the definite article, or when it has another 'plural' determiner.(As a noun it is always considered plural.)
There are now over four million unemployed in this country. (Noun)
Well, in your definition, you just repeated the word being defined; I assume the authors couldn't afford such a waste of space.
I found that definition in ldoceonline.com, in the thesaurus section:Well, in your definition, you just repeated the word being defined; I assume the authors couldn't afford such a waste of space.