I am not sure I understand the question. "Lightning" has two syllables-- light, and ning. Nothing else was added to it. The word is a noun, referring to flashes of electricity in the sky during a storm, often accompanied by the loud sound of thunder.
Lightning is stressed on the first syllable.
Lightning is a two syllable word spoken as light-ning.
The first syllable
Yes, lightning is two syllabels: light-ning.
Neither it is an added syllable
prefix
suffix
prefix
prefix
prefix
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Disastrous has three syllables but, yes, an extra syllable is often added in speech due to the relationship between this word and the word disaster.