Ring up about second musical work (4)
I believe the answer is:
opus
'musical work' is the definition.
(I've seen this before)
'ring up about second' is the wordplay.
'ring' becomes 'o'.
'about' says the letters should be written backwards.
'second' becomes 's' (common abbreviation).
'up' in reverse letter order is 'pu'.
'o'+'pu'+'s'='OPUS'
(Other definitions for opus that I've seen before include "(Numbered) musical composition" , "Creative work, eg in writing, art or music" , "Soup (anag.)" , "Major work" , "Composition - magnum __" .)