The noun 'Sapphire' (upper case S) is a proper noun, the name of a person.
The noun 'sapphire' (lower case s) is a common noun, a general word for a bright blue precious stone; a general word for a shade of blue.
A noun used to describe another noun is called an attributive noun.
Examples:
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Some noun color descriptions include "crimson," "sapphire," "emerald," and "magenta." These nouns are used to vividly and specifically describe different hues and shades in the color spectrum.
A noun used to describe another noun is called an attributive noun (or noun adjunct).Examples of nouns used to describe the noun diamond are:marquis diamondfair trade diamondbaseball diamondengagement diamond
Description
The abstract noun forms for the verb to describe are description and the gerund, describing.
No, "loose" is not a noun. It is typically used as an adjective to describe something not firmly fixed in place or not tightly packaged.