Start of record I'm frightened to hum (4)
I believe the answer is:
reek
'hum' is the definition.
(thesaurus)
'start of record i'm frightened' is the wordplay.
'start of' indicates taking the first letters.
'i'm frightened' becomes 'eek' (expression of fear).
The first letter of 'record' is 'r'.
'r'+'eek'='REEK'
'to' acts as a link.
(Other definitions for reek that I've seen before include "Does Croagh Patrick smell?" , "hum a lot!" , "Smell strongly" , "Smell badly" , "Smell pungently" .)