Some words, depending on how they're used, can be used as different parts of speech.
i.e a noun in one case and a verb in another.
Here's a couple examples: Top, Quiet, Fast
noun in "the spinning top fell over"
adjective in "the top shelf"
adjective in "she's a quiet person"
noun in "I need peace and quiet" or "please keep quiet"
noun in "they completed a two day fast"
adjective in "the new car is fast"
The process itself is called "conversion" or "zero derivation" . It refers to the process of changing a word's part of speech without any change to its morphology.
Conversion normally involves changing a word's syntactic category without any concomitant change of form, as in the creation of the verb humble from the adjective humble or of the noun attempt from the verb attempt
from Huddleston, R, and GK Pullum. 2002. The Cambridge Grammar of English. Cambridge
The words that experience conversion may be referred to as "zero-derived words".
There are words like record or permit which can be used as a noun or verb. They have the same spellings and the same (or lets say related) meanings, but the stress is moved to a different syllable, so they are a little different in pronunciation. This process is called "initial-stress-derivation":
Initial-stress derivation is a phonological process in English that moves stress to the first syllable of verbs when they are used as nouns or adjectives. (This is an example of a suprafix.) This process can be found in the case of several dozen verb-noun and verb-adjective pairs and is gradually becoming more standardized in some English dialects, but it is not present in all. The list of affected words differs from area to area, and often depends on whether a word is used metaphorically or not. At least 170 verb-noun or verb-adjective pairs exist. Some examples are:
- record: as a verb, "Remember to recórd the show!".
- record: as a noun, "I'll keep a récord of that request."
Your examples above are all homonyms. Homonyms are words that are spelled and pronounced the same but have different meanings.
Taking "top" as a single example; as a noun it can be used to describe an item of clothing (in UK English anyway) and obviously that is something entirely different to a "spinning top". So what you have are two different things that are spelled and pronounced the same. The fact they have the same root meaning is certainly relevant, but doesn't make them the same.
One comment suggested that they are "homophones", but that isn't completely accurate if they are spelled the same. True, a homonym is also by definition a homophone, but two words can be considered homophones if they simply sound the same (for example sea and see). If they are spelled and sound the same they are homonyms.
The reason I feel this is the most appropriate answer is because "homonym" accurately describes the words above regardless of whether or not they are different word classes (what you call "parts of speech", eg nouns, adjectives, etc).
Also two words can be described as homonyms whether or not the words have the same derivation. For example, "mine" as a noun for an underground excavation is of French or possibly Celtic origin. The adjective "mine" meaning to dig such an excavation is clearly derived from it. However, "mine" as a possessive pronoun is of Germanic origin, so it cannot be referred to as a derivation. However, all three are homonyms.
