"Whichever" is an indefinite pronoun. It is typically used to refer to any from a limited set of things or options.
"Everyone" is one word.
The word "without" consists of one word.
Yes, "schoolchildren" is one word.
Starfish is one word.
The word house and the word horse (whichever you were trying to spell) are both common nouns.
Whichever one you like best.
Your answer would be: "immediate", "immediately", "promptly", "instantly". They're synonyms, so use whichever word you choose.
Whichever one happens to be above the rest.
Whichever one you want the most
Whichever one you like the best!
operating cycle or one year, whichever's longer
People go to whichever college accepts them and whichever one they want to - it makes no difference at all which kindergarten you go to.
Whichever one there's the least of.
Whichever one was born first.
Whichever one suits you better.
whichever one you think