Unlimited shapes obstruct unbroken passage, in theory (8)
I believe the answer is:
wormhole
'passage in theory' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'unlimited shapes obstruct unbroken' is the wordplay.
'unlimited shapes' becomes 'orm' (I can't explain this - if you can you should give a lot more credence to this answer).
'obstruct' is an insertion indicator (inserted letters interrupt or obstruct the word).
'unbroken' becomes 'whole' (I've seen this in another clue).
'orm' inserted into 'whole' is 'WORMHOLE'.
Can you help me to learn more?
(Other definitions for wormhole that I've seen before include "could be ruined?" , "Space made by burrowing creatures in fruit, wood, books etc" , "Cavity make in wood by burrowing larvae" , "Hypothetical tunnel in space-time" , "Space made by burrowing limbless creature" .)