Atheism is specifically a rejection of theism. Atheist is derived from the greek word Atheos which means A=Without theos=Gods( this was actually a pejorative used against early christians by Roman Pagans prior to Edict of Milan) if we examine the word Atheist the A =Without. Theism= a belief in a personal God so to put it literally an Atheist is one who posses no belief in a personal God. Theism in contrast to Deism (a non personal God who cares nothing for humans but set up the collective laws for creation) See Spinozea.
So by this line of reasoning it could very well be argued that a Deist is an Atheist in practice. As deism was created as a rejection of Theism. See Thomas Jefferson.
(This is shorter version of an old post titled Atheism, Theism and Deism explained, which goes into greater detail, if anyone is interested)