Do they all come from the same root word?
Kind of! All but the animal are related:
- Bull (refering to the animal and all that) --comes from Old English bula "a steer" which came from Old Norse boli "bull", both of which came from bullon, the Germanic stem which means to roar. This is also the root of the English word boulder.
- Bull (refering to the papal declaration)--comes from teh Latin bulla "sealed document" (which used to be the word for the seal itself), coming from Latin bulla meaning "round thing, knob" which might have come from Gaulish. Words like buttocks, bubble, boil, bowl and even bag might have come from this same root.
Which leads into...
- Bullet--This comes from that same aforementioned Latin bulla. It went into French, balle meaning "ball" got the diminuitive ending -ette for "little ball" and tada! Note: boulette in Modern French means "cannon ball."
- Bulletin--This came from when the Latin bulla meant bill (Medieval Latin) and took the French and Italian diminuitive forms -ette and -ino. ! Note: Popularized by their use in the Napoleonic Wars as the name for dispatches sent from the front meant for the home public (which led to the proverbial expression "as false as a bulletin"). The first record of bulletin-board is from 1831.