The word Mahershalalhashbaz has 18 characters and is the longest word in the Bible. It's meaning is taken from the King James Version of the Bible and is: Isa 8:1 Moreover the LORD said unto me, Take thee a great roll, and write in it with a man's pen concerning Mahershalalhashbaz. Isa 8:3 And I went unto the prophetess; and she conceived, and bare a son. Then said the LORD to me, Call his name Mahershalalhashbaz.
There are two words in the Bible that are 18 letters, they are MAHER-SHALAL-HASH-BAZ (Isaiah 8:1) and JONATH-ELEM-RECHO-KIM, which is found in the title of Psalm 56. There is one word that is 17 letters long and eight words that are 16 letters long.