The word "in" is only particularly an adjective when used colloquially for "modern" (the in crowd, the in fashion) or to mean known or used by a certain group (an in reference or inside reference, as with inside information).
It is also used trivially for "in door" and "out door" which are one-way passageways connecting to an interior space or kitchen.
All other uses are selective forms of the adjective inner or the adverb inward.
The adjective form for the verb to use is the past participle, used (a used car).The adjective form for the noun use is useful(useful information).
Happy is already an adjective.
Yes, you can use the adjective dramatic.
Yes, It Almost Has The Meaning As The Adjective.
Yes, the term 'untidy clothes' is a correct use of the adjective.
"Obsolete" is an adjective. It describes something that is no longer in use or outdated.
a good adjective is ugly
the adjective is captive - the noun is captivity
Yes you can use it as an adjective by saying someone is 'arachnophobic'
An adjective describes a noun.
never
Use the suffix -ly when you want to change an adjective to an adverb. Ex: The girl is beautiful; adjective The girl spun around beautifully; adverb