1. spend:
to use money to buy or pay for something
2. spend:
use money to buy or pay for something
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word:
definition
(Why is 'to...' used in a dictionary for the definition of each word? What about #2? Can we use as in #2 as the definition of each word?)
I think because it doesn't make sense to say, "Spend is use money..." It does make sense to say, or write, "Spend is to use money..." It could also be properly (sensibly) phrased, "Spend is the use of money to buy or pay for something." Without the prepositions, neither would make sense.
In dictionaries, the use of "to" in the definition of each word is a way to explain how the word functions in a sentence or its usage. It helps to provide context and clarify the meaning.
In the example you provided, "#1 spend: to use money to buy or pay for something," the "to" is used to indicate the purpose or intention behind spending money, which is to buy or pay for something. It shows the action or goal associated with the word "spend."
On the other hand, in "#2 spend: use money to buy or pay for something," the "to" is not explicitly stated, but it implies the same meaning as in #1. The word "use" is equivalent to "to use," and therefore, the definition is still providing the same explanation.
So, you can use "#2 spend: use money to buy or pay for something" as an alternative and equally valid way to define the word "spend." However, the inclusion of "to" in the definition (e.g., "#1 spend: to use money to buy or pay for something") is beneficial as it explicitly connects the action of spending money to its purpose.