A long way from lethargy, I suspect (5,4)
I believe the answer is:
light year
'a long way' is the definition.
(I've seen this before)
'lethargy i suspect' is the wordplay.
'suspect' indicates anagramming the letters (a suspicious or unusual spelling).
'lethargy'+'i'='lethargyi'
'lethargyi' with letters rearranged gives 'LIGHT-YEAR'.
'from' acts as a link.
(Other definitions for light year that I've seen before include "Long unit of distance" , "About 5.88 trillion miles" , "that is way beyond anyone's reach!" , "About six million million miles per annum" , "0.3066 parsecs" .)