Word puzzle bringing on a vexed moment, by the sound of it (8)
I believe the answer is:
acrostic
'word puzzle' is the definition.
(I've seen this in another clue)
'a vexed moment by the sound of it' is the wordplay.
'vexed' becomes 'cros' (I am not sure about this - if you are sure you should believe this answer much more).
'moment' becomes 'tick' (both can mean a very short amount of time).
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'tick' is a homophone of 'tic'.
'a'+'cros'+'tic'='ACROSTIC'
'bringing on' acts as a link.
Can you help me to learn more?
(Other definitions for acrostic that I've seen before include "Poem with word(s) reading downwards" , "Legal document" , "a little puzzling" , "Socratic kind of old word puzzle" , "Verse where eg the first letters in each line form a word or message" .)