In (proper!) UK English, it's written with a hyphen. I don't know about US English or other variations of English. If you Google it, you'll find all three forms widely used!
Extracurricular is one word.
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The word extracurricular comes from the two words " extra & credit ". So since there is only one ful word that is in the word " extracurricular " extra is the root word.
Contracted words.
Chess player is written as two words.
Two words.. one hundred.
"all day" is typically written as two separate words.
One and two hundredths.
It is not one nor two words. It is hyphenated, just as it is written in the question.
Businessmen is often written as one word. It can be two words or even hyphenated
"All right" is written as two words and "already" is one word.However, "alright" (the informal variant of all right) is written as one word.
Underdeveloped should be written as one word, not two words or hyphenated. I hope this answered your question. :)