Beginning to groan in dreadful lament (5)
I believe the answer is:
dirge
'lament' is the definition.
(synonyms)
'beginning to groan in dreadful' is the wordplay.
'beginning to' indicates taking the first letters.
'in' indicates putting letters inside.
'dreadful' becomes 'dire' (synonyms).
The first letter of 'groan' is 'g'.
'g' put into 'dire' is 'DIRGE'.
(Other definitions for dirge that I've seen before include "Dreary song" , "Threnody" , "Funeral song" , "Funereal hymn" , "Requiem" .)