The words damming, damning sound the same but have different meanings and spellings. Why do damming, damning sound the same even though they are completely different words?
The answer is simple: damming, damning are homophones of the English language.
Present participle of <xref>dam</xref>.
That condemns or exposes to condemnation or damnation: as, <em>damning</em> proof; <em>damning</em> criticism.
That damns; damnable.
Present participle of <xref>damn</xref>.
Property which <xref>damns</xref>.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License., from The Century Dictionary., from the GNU version of the Collaborative International Dictionary of English. and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").