The part of speech is an important part of the identity of every single word in the English Language. Some words can function only as one part of speech. They never change. They can perform one job in the sentence, and no other. Here are a few examples of words that always act as one part of speech:
George just celebrated his second birthday. (George is a noun.)
He loved receiving many presents! (He is a pronoun.)
The games were also fun, and George played all of them. (Were and played are verbs.)
Gina sang a lovely song to George. (Lovely is an adjective.)
Many words may change their part of speech depending upon the job they do in a sentence. Look at these examples:
Chichester is my home. (home = noun)
Please write your home address on the form. (home = adjective)
Go home now! (home = adverb)
They work until noon. (work = verb)
All the work has been completed. (work = noun)
The work room is very disorganised. (work = adjective)
James just walked by. (by = adverb)
By the lake, the cabins are older. (by = preposition)
How can you tell which part of speech you are dealing with? Check the dictionary. After the word, you will see the part of speech and then the definitions that match. Usually, the part of speech is abbreviated. (A key to the abbreviations often appears somewhere in the dictionary or on the website.)
Here is an example of a dictionary entry for a word that is always the same part of speech:
now adv. at the present time 'John is busy now'.
In that entry, now is identified as an adverb. An adverb tells when, where, why, or how something happened. Adv. is short for adverb.
If a word may act as more than one part of speech, the definitions appear next to the part-of-speech label. Glance at this example:
n. an entertainment event 'The show begins at 8:00'.
v. to reveal or to display 'Sally may show her stamp collection to the class tomorrow'.
The label and the example sentences help you decide how to use a word in any sentence.