"Backwards" is an adverb: "The car moved slowly backwards along the street."
"Backward" is an adjective. "Backwards" and "backwardly" are adverbs and "backwardness" is a noun.
"-ward" isn't any part of speech. It's a suffix.
The word postic is an adjective. It is a word that means backward but this term is no longer used in present day English.
When the suffix "-ward" is added to a word, it typically creates an adverb indicating direction or movement. For example, "backward" or "toward."
snell
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
what part of speech is beneath
adverb
The part of speech for "explicit" is an adjective.
The part of speech for "lecturer" is a noun.