It acts as a noun-modifier.
The past participle form of the word "use" is "used."
Used is the past participle; using is the present participle.
The past participle for "am using" is "have used."
"Use" is a regular verb; therefore, its past participle is "used".
The word sitten is the past participle of sit. It is used as a verb.
There is no past participle. The idiomatic construction "have to" means "must" and is used as an auxiliary verb. (The verb to have has the past tense had and the past participle had.)
No. -ing is used for the present participle.
The past participle of fashion (used as a verb) is fashioned.
No. When used as a verb, the past participle of coat is coated.
Used (e.g "It had been used for...", "John was used", etc.)
Worse is rarely used as a verb. When it is, the past and past participle is worsed.
The past participle of hear is heard. Past participles are words formed from verbs which can be used as adjectives.