Perhaps ammonia has power to catch the breath (4)
I believe the answer is:
gasp
'catch the breath' is the definition.
(I've seen this before)
'perhaps ammonia has power' is the wordplay.
I cannot quite understand how this works, but
'power' could be 'gas' (I've seen this in another clue) and 'gas' is located in the answer.
A single letter 'p' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'to' is the link.
Can you help me to learn more?
(Other definitions for gasp that I've seen before include "Sudden intake of breath" , "Convulsive breath" , "Draw breath sharply" , "Breathe sharply in amazement, horror etc" , "Struggle for breath with open mouth" .)