These two terms are often used interchangeably, but they are not one and the same. Dethatching refers to the act of removing excess thatch from the lawn while aeration refers to poking holes in the soil to help improve drainage and nutrient availability. Most homeowners have problems with both thatch and compaction, so aeration will usually take care of both issues.  However, if it’s just a thatch build-up (and more than ½” of thatch) that is causing you trouble, using a dethatching tool will be much more effective.