Very reliable person's powerful tractor? (5,2,8)
I believe the answer is:
tower of strength
'powerful tractor?' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tower of strength that I've seen before include "One very reliable" , "one you can depend on" , "tugboat?" , "Person giving support" , "Powerful tractor" .)