Headline: “Millions trapped in hopeless careers” (8)
I believe the answer is:
screamer
'headline' is the definition.
(screamer is a kind of headline)
'millions trapped in hopeless careers' is the wordplay.
'millions' becomes 'm' (abbreviation).
'trapped in' is an insertion indicator.
'hopeless' is an anagram indicator.
'careers' is an anagram of 'screaer'.
'm' inserted into 'screaer' is 'SCREAMER'.
(Other definitions for screamer that I've seen before include "South American bird with loud, harsh cry" , "powerful shot" , "Remarkable thing; noisy person; large water bird" , "express delivery" , "Sensational newspaper headline - mere scar (anag)" .)