Gossip leads to torment and lamentable knowledge (4)
I believe the answer is:
talk
'gossip' is the definition.
(talk is a kind of gossip)
'leads to torment and lamentable knowledge' is the wordplay.
'leads to' indicates taking the first letters.
The initial letters of 'torment and lamentable knowledge' is 'TALK'.
(Other definitions for talk that I've seen before include "Utter" , "Gas" , "that's said to be cheap" , "Converse" , "Gossip - lecture" .)