The words gased, gassed, gast sound the same but have different meanings and spellings. Why do gased, gassed, gast sound the same even though they are completely different words?
The answer is simple: gased, gassed, gast are homophones of the English language.
Third-person singular simple present indicative form of gas.
Plural form of gas.
Slang Drunk or intoxicated.
Obsolete To frighten; scare.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.