Cart may be the name of the thing—the noun—that Junior is conveyed or carried in, as in definition 2. And it may also be the conveying or carrying of Junior from one place to another—the verb—as in definition 3. You can use cart both as a noun and as a verb.
But think about car: "The car is headed for the main road." Car is most certainly a thing named, a noun. But try using it as a verb: "They will car him to the station." Or "They carred to Mexico last summer." It can't be done, and the main entry for car tells you so:
car n. 1 Any vehicle used to carry people or goods, especially an automobile. 2 A vehicle for use on rails, as a railroad car or a streetcar. 3 The enclosed platform on which people or things are carried in an elevator.
All these definitions are noun definitions. You see that car is not used as a verb.
Although you would not be likely to be confused about cars, suppose you came across a new word and had to use it properly. First you hear a friend say, "My little brother's prattle kept me from finishing my homework." In this sentence, prattle is the name of the special noise that the small boy is making, so it is a noun. But can you use prattle as a verb? Can you say to another friend, "Junior prattled away and kept Archie from finishing his homework"? You must find out whether it is like car and can be used only as a noun or whether it is like cart and can be both a noun and a verb.
prat-tie v. prat-tied, prat-tling, n.
1 v. To talk foolishly or like a child. 2 n. Foolish or childish talk. 3 n. The sound of childish speech, or a sound like it. — prat'tler n.
The entry tells you that prattle can be used both ways.
ADJ. USE AND N. USE
After you begin to look at the parts of speech labels in your dictionary entries, you will find even more answers to "Can I use it?" For example, how many ways can you use the word mail?
I will mail your letter. (Used as a verb.) The postman brought the mail early. (Used as a noun.) He drove the new mail truck. (Used as an adjective.)german vienna language course
In the third sentence you can see mail being used in a special way—adjectivally. Your dictionary tells you about using a word this way by putting adj. use right after the definition number. Here is how it looks in the main entry for mail:
mail1 1 n. Letters or parcels sent or received through a governmental postal system. 2 n. The postal system itself. 3 n. Postal matter collected or delivered at a certain time: the morning mail. 4 adj. use: a mail truck. 5 v. To send by mail; put into the mail.
Definition 4 lets you know that what may look like the noun defined in definition 3 can be used adjectivally. Usually, as here, no definition is needed. An illustrative phrase shows you the use and meaning.немецкого языка курсы вена
In very much the same way, what looks like an adjective can sometimes be used as a noun. You can see this happening in the first two definitions of rich:
rich [rich] adj. 1 Having a lot of money, goods, or property; wealthy. 2 n. use: Rich people: The rich are sometimes generous.használt csöves erősítő
Rich, which is usually used adjectivally, can have a noun use. You don't have to say "rich people" every time. You can quite properly say "the rich" and mean the same thing.