Crossword Genius

Building obstacle (5)

Ross

I believe the answer is:

block

I'm a little stuck... Click here to teach me more about this clue!

This might be a double definition.

'building' is the first definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe you can see an association between them that I don't see?

'obstacle' is the second definition.
(thesaurus)

Can you help me to learn more?

(Other definitions for block that I've seen before include "Jam" , "City area; prevent flow" , "Mass of wood etc - set of buildings" , "Cube" , "cake?" .)

I've seen this clue in The Mirror.
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