Block entered back to front (5)
I believe the answer is:
ingot
'block' is the definition.
(I know that ingot is a type of block)
'entered back to front' is the wordplay.
'entered' becomes 'ingo' (I can't explain this - if you can you should give a lot more credence to this answer).
'back to' indicates one should take the final letters.
The final letter of 'front' is 't'.
'ingo'+'t'='INGOT'
Can you help me to learn more?
(Other definitions for ingot that I've seen before include "Bar, brick of metal" , "Mass of metal, especially gold or silver" , "Piece of precious metal" , "Gold Stick" , "Moulded metal bar" .)