Dive in the middle? It is breath-taking! (4)
I believe the answer is:
lung
'it is breath-taking' is the definition.
The definition suggests a singular noun which matches the answer.
'dive in the middle?' is the wordplay.
'dive' becomes 'plunge' (synonyms).
'in the middle?' means to look at the middle letters (I've seen 'in the middle' mean this).
The middle of 'plunge' is 'LUNG'.
Can you help me to learn more?
(Other definitions for lung that I've seen before include "breather" , "Organ providing oxygen to the blood" , "Organ used for breathing" , "Breathing apparatus" , "Of sound mind" .)