The words lacks, lax sound the same but have different meanings and spellings. Why do lacks, lax sound the same even though they are completely different words?
The answer is simple: lacks, lax are homophones of the English language.
Plural form of lack.
Third-person singular simple present indicative form of lack.
Lacking in rigor, strictness, or firmness. See Synonyms at negligent.
Not taut, firm, or compact; slack. See Synonyms at loose.
Loose and not easily retained or controlled. Used of bowel movements.
Linguistics Pronounced with the muscles of the tongue and jaw relatively relaxed, as the vowel (ĕ) in let.
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.