He is standing still.
(Is 'still' an adjective or an adverb?)
Is it modifying a noun(adjective) or a verb(adverb)?
In this sentence, it's an adjective -- modifying the subject "He."
http://dictionary.reference.com/browse/still
In the sentence "He is standing still," the word "still" is functioning as an adverb. It describes how he is standing, indicating that he is not moving. As an adjective, "still" would describe a static condition or lack of movement, such as "a still lake" or "a still night."
To determine whether "still" is functioning as an adjective or an adverb in the sentence "He is standing still," we need to understand its role in modifying the verb "standing."
In this case, "still" is functioning as an adverb because it is describing the manner in which he is standing. Adverbs often modify verbs, adjectives, or other adverbs. In this sentence, "still" modifies the verb "standing" by adding the meaning that he is not moving or is stationary.