A call at first clear and sharp (5)
I believe the answer is:
acrid
'sharp' is the definition.
(I've seen this before)
'a call at first clear' is the wordplay.
'at first' says to take the initial letters.
'clear' becomes 'rid' ('rid' can be a synonym of 'clear'**).
The first letter of 'call' is 'c'.
'a'+'c'+'rid'='ACRID'
'and' acts as a link.
(Other definitions for acrid that I've seen before include "Nastily pungent" , "Unpleasantly strong-smelling" , "Strong and sharp-smelling" , "Astringent" , "Sour, pungent" .)