Catch your breath at first glance of snake (4)
I believe the answer is:
gasp
'snake' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'catch your breath at first glance' is the wordplay.
'catch your breath' becomes 'asp' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'at' means one lot of letters go next to another (I've seen this in other clues).
'first glance' becomes 'g' (ast letter of 'glance').
'asp' after 'g' is 'GASP'.
'of' is the link.
Can you help me to learn more?
(Other definitions for gasp that I've seen before include "Fight for breath" , "Draw breath sharply" , "Show amazement" , "Sudden intake of breath" , "Convulsive breath" .)