from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Inability to concentrate.
from The Century Dictionary and Cyclopedia
- n. Lack of power to keep the attention fixed on any subject; an extreme degree of mind-wandering.
Sorry, no etymologies found.
I have seen cases which were regarded as instances of aprosexia,  the lack of the power of concentration being attributed to adenoid vegetations, but in which the defect might, with at least as much reason, have been referred to the play of sexual ideas.