I don’t mean synonyms for buttocks. Well, let me give you some examples…
Asparagus Gustav and Augustus moon the audience.
Asymetrical One buttock is larger than the other.
Ascot A camp stool.
I’m sure there’s one for the Attorney General, but I haven’t found it yet.
Assert A mint for your farts.
An exotic dancer is an asset to music.
AskNott ~ A muscular tense area on the butt of the OP.
Astronomy ~ The study of the great butts & heavenly bodies.
Astounded ~ What I become when discovering a great butt. 
**asphyxiate **–to firmly attach one’s buttocks.
Asunder – antonym of prone.
Aspartame - For sweet food without bulging buttocks.
Asgaard – protective pants.
Astute - a fart.
Asymptomatic: “You might be an ass if…”
Assuage: when that ass gets three sheets to the wind.
Aspirate: 'nuff said.
Assess: When you have curves, but not exactly in the right places.
Astrology:
What, you thought lieu was some other sort of doctor?
Aspire: Wishing one had JLo’s body.
Ascertain: To tell someone from behind.
Asphalt: The perfect ass.
Assist The thing that kept Rush Limbaugh from being drafted.
Assad Depression over one’s nether curves.
Asti Spumante See Tubgirl. :eek:
Assimilation Certain fart-lighting mishaps.
Asymptote - When your ass gradually approaches zero as your age approaches infinity.
asterisk – inclined to a hazardous lifestyle; also prone to dangerous dieting techniques
I regret that I have but one asterisk for my country.
Aspire - The place where Vikings cremated their buttocks
Astride - immovable constipation
Assorted - from largest to smallest by cheek size
Aspic - like those things for removing stones from horses hooves, only different
Ashore ~ A callgirl that does it all.
Ascertain ~ When you are 100% sure that it’s an ass.
Ashamed ~ Feelings you have when you have no ass. (or get no ass)
Assess ~ When your butt crack is S shaped.
Asimilate ~ Mimicking another’s ass.
Asbestos ~ A rump so fine, you can’t flame it in The Pit. 
[sub]I’m still chuckling over “Asterisk for my country”[/sub]