To cross the street is an easy undertaking (8)
I believe the answer is:
walkover
'undertaking' is the definition.
(I know that walkover is a type of undertaking)
'to cross the street' is the wordplay.
'to cross' becomes 'walk' (walking is a kind of crossing).
'the street' becomes 'over' (I can't explain this - if you can you should believe this answer much more).
'walk'+'over'='WALKOVER'
'is an easy' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for walkover that I've seen before include "Piece of cake - child's play" , "Unopposed victory" , "victory's easy" , "easy win" , "Uncontested race" .)