Involving much effort (9)
I believe the answer is:
strenuous
(Other definitions for strenuous that I've seen before include "requiring much effort" , "Very active" , "Hard" , "Laborious" , "with difficulty" .)
I believe the answer is:
strenuous
(Other definitions for strenuous that I've seen before include "requiring much effort" , "Very active" , "Hard" , "Laborious" , "with difficulty" .)