a sesquipedalian
Arithemetic is for losers who want to use big words. It is correctly called "math!"
Someone who uses unnecessary big words when speaking or writing is often referred to as a "sesquipedalian." This term is derived from the Latin word "sesquipedalis," meaning a foot and a half long, and is typically used in a derogatory sense to describe someone who overly complicates their language.
Enormous is most commonly used word to describe big before someone uses colossal.
A mispronunciation of "obiter dictum" by someone who uses big words without determining correct details. I have also heard it mangled as "obenedictum".
A person who uses big words incorrectly could be described as pretentious or as having a poor command of language.
This type of person is commonly referred to as a "sesquipedalian" or someone who uses "sesquipedalianism," which means the excessive use of long words. They may also be described as pretentious or condescending in their communication.
Hippopotomonstrosesquippedaliophobia means the fear of big words, so he would be a hippopotomonstrosesquippedaliophobe.
A person who uses big words incorrectly is often referred to as a malapropism. This term refers to the mistaken use of a word in place of a similar-sounding one with a different meaning.
Big is an adjective. Words that modify adjectives are called adverbs. Really is an adverb that can modify big.
sesquipedalian : given to or characterized by the use of long words It's an adjective not a noun.
big words
Descriptor words might be stout, tubby, big boned, or big for his age.