needing and using much energy and thought

difficult, hard to endure

requiring much effort, strength, skill or ability

hard on someone; hard to do

needing, showing, great effort

hard, difficult

slow and troublesome; not easy or natural

difficult to understand, unclear

needing much effort

difficult; requiring hard labor

using or needing great effort

difficult; requiring hard work

(moving) in the opposite direction to the stream or current

hard on someone; hard to do

tiring; long and dull

burdensome