Difficult words to learn? Bad luck! (4,5)
I believe the answer is:
hard lines
'bad luck' is the definition.
(I've seen this before)
'difficult words' is the wordplay.
'difficult' becomes 'hard' ('hard' can be a synonym of 'difficult').
'words' becomes 'lines' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'hard'+'lines'='HARD LINES'
'to learn?' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for hard lines that I've seen before include "Tough" , "Script full of tongue-twisters?" , "Bad luck" .)