(a.) Having a single purpose; hence, artless; guileless; single-hearted.

absent absentminded absorbed in abstracted bemused buried buried in buried in thought castle-building caught up in concentrating contemplating contemplative daydreaming daydreamy deep devoted devoted to dreaming dreamy drowsing ecstatic elsewhere engaged engaged in thought engrossed engrossed in engrossed in thought enmeshed in entangled in far-gone faraway half-awake immersed immersed in immersed in thought implicated in in a reverie in the clouds intent intent on introspective involved involved in lost lost in lost in thought meditating meditative monomaniacal monopolized mooning moonraking museful musing napping nodding oblivious obsessed occupied pensive pipe-dreaming preoccupied rapt single-minded somewhere else stargazing studious studying submerged in swept up taken up taken up with tied up in totally absorbed transported unconscious woolgathering wrapped wrapped in wrapped in thought wrapped up wrapped up in