Bellybuttons would be the longest word I can think of beginning with a 'b' and ending in an 's'.
bob
INDUSTRIALIZATION
firetruck
Acetylcholinesterase is a 20 letter word. It is a chemical compound.
The real song for ack is Brooklyn's song.
poo poo ack
The word Pontiac is pronounced as "PON-tee-ak."
The longest ones I could find in Webster's Second International dictionary are 17 letters long: antiagglutinating autoagglutinating
The secret password for The Loyal Order of Water Buffaloes on The Flintstones was: "Ack, Ack, A-Dack"
Scoop, Soup, and others, I'm not 100% sure about the rest though
That's an interesting question. I dont' know for sure, but the longest one I can think of right now is Electric. Hope I helped!