Tennyson, losing heart, junked poem (6)
I believe the answer is:
sonnet
'poem' is the definition.
(type of poem)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for sonnet that I've seen before include "Fourteen-lined verse" , "Fourteen-line 11" , "14-line poem" , "Poem of 14 lines - Shakespeare wrote lots" , "Short poem with 14 lines" .)