The term 'false feet' is the plural form; the singular form is 'false foot'.
The plural spelling is Ellises.
The plural spelling of luxury is luxuries.
True. When making a singular noun plural, the spelling often changes. This can involve adding -s, -es, or -ies to the end of the word, or changing the internal vowel or consonant.
the plural is Christmases
The correct spelling of the plural of cyclist is cyclists.
The plural of flight is flights.
The plural of society is societies.
The plural of kangaroo is kangaroos.
The plural of tornado is tornadoes.
The spelling Spurius is a proper noun, a Latin given name, with the English plural Spuriuses.The spelling spurious is an adjective, and has no plural.
That is the correct spelling of the plural noun "coverages" (usually insurance).
That is the correct spelling of the word "sky" (plural skies).