"absent in mind, distracted from present reality by intellectual activity," 1640s, past-participle adjective from abstract (v.). Related: Abstractedly.
An absent man is one whose mind wanders unconsciously from his immediate surroundings, or from the topic which demands his attention; he may be thinking of little or nothing. An abstracted man is kept from what is present by thoughts and feelings so weighty or interesting that they engross his attention. [Century Dictionary]