I'd call it a fat, 100g contains 8.5g carb, 2g protein, and 14.66g fat for 174 cals (so probably 1/2 a large). That refers to the edible portion, and I've never actually weighed the pitt....
I like it in salads. I've read that it helps other nutrients from veg to be absorbed... but that was on some "avocado grower's" page, so it might just be bs.