Attentiveness (13)
'attentiveness' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for interest that I've seen before include "Excite the curiosity of (someone)" , "Care" , "Return" , "Stake; concern deeply" , "Sum paid on a loan" .)
'attentiveness' is the definition.
(I have seen 'Complete attentiveness' mean 'concentration' so perhaps 'attentiveness' could also mean 'concentration')
This is all the clue.
(Other definitions for concentration that I've seen before include "A close gathering; mental focus" , "Application" , "Focussing" , "Complete attentiveness" , "Absorption" .)