My gosh. Sigh. Please everyone read this.

[link to beliefmap.org (secure)]
Some atheist figureheads—notably Matt Dillahunty—have promoted the idea that, in addition to the word “non-theist”, the word “atheist” is also properly defined as: a person who lacks belief in God(s). This “lack of belief” definition would include agnostics under the definition of atheist, and so would crowd out defining atheism as the positive belief that God does not exist. (This community suggests calling a positive belief in God's non-existence, “strong atheism”). At least as far as there can be an answer to the question of whether a term is being used properly, is this community correct?

Academic sources unanimously answer “NO”
It might come down to the level of precision users want. In academic settings, where precision is aimed for, the answer is unanimous:
• Stanford Encyclopedia of Philosophy (2011): “‘Atheism’ means the negation of theism, the denial of the existence of God.” [Atheism and Agnosticism, Online]
• Encyclopedia of Unbelief (2007), p. 88: “In its broadest sense atheism, from the Greek a (‘without’) and theos (‘deity’), standardly refers to the denial of the existence of any god or gods.”
• Encyclopedia of Philosophy 2nd ed. (2006), p.358 [in vol. 1 of 10]: “According to the most usual definition, an atheist is a person who maintains that there is no God, that is, that the sentence ‘God exists’ expresses a false proposition. In contrast, an agnostic maintains that it is not known or cannot be known whether there is a God”
• Oxford Companion to Philosophy, New Ed. (2005), p. 65: “Atheism is ostensibly the doctrine that there is no God. Some atheists support this claim by arguments. But these arguments are usually directed against the Christian concept of God, ... Agnosticism may be strictly personal and confessional—‘I have no firm belief about God’—or it may be the more ambitious claim that no one ought to have a positive belief for or against the divine existence.”
• Blackwell Dictionary of Western Philosophy (2004), p. 530: “The belief that God – especially a personal, omniscient, omnipotent, benevolent God – does not exist.”
• Routledge Encyclopedia of Philosophy (1998), entry by William Rowe: “As commonly understood, atheism is the position that affirms the nonexistence of God. So an atheist is someone who disbelieves in God, whereas a theist is someone who believes in God. … the common use of ‘atheism’ to mean disbelief in God is so thoroughly entrenched, we will follow it. We may use the term ‘non-theist’ to characterize the position of the negative atheist.”