What is the longest word that most English dictionaries accept?

I work best on a deadline so I start projects close to their due date.

A.) Antidisestablishmentarianism

A.) Antidisestablishmentarianism

I work on the tasks that I enjoy most first.

B.) Pneumonoultramicroscopicsilicovolcanoconiosis

B.) Pneumonoultramicroscopicsilicovolcanoconiosis

I work on the tasks that I enjoy most first.

C.) Floccinaucinihilipilification

C.) Floccinaucinihilipilification

I work on the tasks that I enjoy most first.

D.) Hippopotomonstrosesquipedaliophobia

D.) Hippopotomonstrosesquipedaliophobia