فَأُمُّهُۥ هَاوِيَةٌ ٩
Sentence structure
فَ introduces the result. أُمُّهُۥ is a nominative subject with possessive هُ, and هَاوِيَةٌ is its nominative predicate.
Ayah summary
His dwelling will be a deep abyss.
فَأُمُّهُۥ — then his abode
Grammar: Result فَ precedes feminine nominative subject أُمُّ; هُ is possessive.
هَاوِيَةٌۭ — is the Abyss
Grammar: An indefinite feminine nominative active-participle noun functioning as predicate.