* Noun: This is the most common usage. It refers to the central part of a seed or grain (e.g., "the kernel of corn").
* Noun: It can also refer to the core or essential part of something (e.g., "the kernel of truth").
* Noun: In computing, it refers to the core of an operating system.
* Adjective: Less commonly, it can be used as an adjective meaning "pertaining to a kernel" (e.g., "kernel corn").
To determine the part of speech, you need to look at the context of the sentence.