A pea swallowed on rising with blockage of the airway (6)
I believe the answer is:
apnoea
'a pea' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see a link between them that I can't see?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for apnoea that I've seen before include "Partial suspension of breath, in sleep say" , "A stoppage of breath" , "Transient cessation of breathing" , "Asphyxia" , "Temporary suspension of breath, as in sleep say" .)