The killing curse is Avada Kedavra, but you must use a wand in order to perform this spell, like all others.
Gillyweed
A little, like the H word and D word
the hanged man
Grindylows.
The word 'muggle' has a number of meanings. In the Harry Potter books it is defined as someone who has no magical skills or abilities. It is also a term used for marijuana.
Gillyweed
werewolf
butterbeer
Elixir of life
cuiryotis -> curiosity
Madam Hooch.
Peppermint toads
Tom Felton works.
Blast-Ended Skrewt
If you are referring to the "Harry Potter" books by J.K Rowling, Harry was a fictional character with the powers of magic and wizardry. If you are referring to the word "potter," it refers to a skilled craftsperson who is able to make vases, bowls, pots, jars and other items, usually out of clay.
The second (and third) word Harry Potter said was "nothing".
No, the closest thing they have to profanity is the word "mudblood" which is unique to the Harry Potter universe. It is a derogatory word used to describe someone raised by a non-magical family. It is treated almost like a racial slur, and people are highly offended when someone says it.