Yes it can be used as an adverb.
It's used in this way to express a lack of something.
It can be, but without is almost always a preposition. It acts like an adjective or adverb when the object is omitted. It is most clearly an adverb when used in the pairing "within and without" which refers to an adjective. It is not clearly an adverb in the usual example "to do without" (something).
The word with is not an adverb; it is a preposition. The word "without" may be an adverb (e.g. to do without, where no specific object is used).
Yes, you can have a sentence without a adjetive or adverb phrase. For example, Her name is Sally. No adverb or adjetive!
Well actually it can be used as an adverb AND a preposition! :)
No sunless is not a adverb it is an adjective what it means is without sun
No, the word infallible is an adjective. The adverb form is "infallibly" (without error).
It is an adjective (without end, or tediously long). The adverb form is endlessly.
Yes, it can be either an adjective or adverb. It can mean continuously, or traveled without stopping.
It can be an adverb (used without an object) or a preposition. There is an old dog that comes around. (adverb) We drove around the block. (preposition)
Direct can be an adjective, a verb and an adverb. Adjective: Without interruption/Straight. Verb: To control/To aim. Adverb: Directly.
The adverb form of the adjective immediate is immediately (right now, without delay).
Yes, it is an adverb. Tirelessly means without becoming fatigued, or implies ceaselessly.