1. Adjective: When "portable" describes a noun, it functions as an adjective.
* Example: "She bought a portable computer." (Describing the noun "computer")
2. Noun: When "portable" is used as the subject or object of a sentence, it functions as a noun. This usage is less common but still possible.
* Example: "The new portable is much lighter than the old one." ("Portable" refers to a specific portable item, likely a computer or device.)
Therefore, "portable" can be either an adjective or a noun.