Learn? I can't — lacking time for observation and application (6)
I believe the answer is:
arnica
'application' is the definition.
(plant used as a medical application)
'learn? i can't lacking time for observation' is the wordplay.
'ARNICA' is hidden in amongst the letters.
But, I am unsure how the hidden word is indicated.
'and' is the link.
(Other definitions for arnica that I've seen before include "something to treat bruises" , "Application" , "Herbal ointment used on bruises" , "Plant preparation to treat bruises" , "A tincture used in treating sprains" .)