The word 'Breakdown' is a/an -

The words breakdown and break down both refer to a failure or a dismantling of some kind, whether it's mechanical, physical, or emotional.
The difference is that, written as one word, breakdown is a noun, referring to the result of the action, while the two-word version, break down, is a phrasal verb that denotes the action leading to the result.
Source: thoughtco.com