In the sentence below...
Scarcity and the need to economize.
- What does the noun 'the Need' mean?
- What does the noun 'the Need to' mean?
- Why do we put the defined article the before the noun Need?
I'm not sure I understand your first question. Have you looked up the word need in a dictionary? If so, what part of the definition doesn't make sense? From Dictionary.com
4 - necessity arising from the circumstances of a situation or case: There is no need to worry.
6 - a condition marked by the lack of something requisite: the need for leadership.
In your second question, "What does the noun 'the Need to' mean?" you have mistaken the "to" for being part of the noun. In reality, it is part of the verb, "to economize." Any time you see "to" immediately before a verb, it indicates the infinitive, or unconjugated form of the verb. "The need to economize" is a noun phrase.
We put the definite article, "the," before the noun to indicate that it actually is a noun. If it said "scarcity and need to economize," then need becomes a plural verb. For instance, consider these example sentences with and without the article,
The government has to deal with scarcity and the need to economize
Local governments are facing scarcity and need to economize.
The first one uses "the need" as a noun while the second one uses "need" as a verb.