Sense of shame reduced deceit over time (5)
I believe the answer is:
guilt
'sense of shame' is the definition.
'guilt' can be an answer for 'shame' (thesaurus). I am not sure about the 'sense of' bit.
'reduced deceit over time' is the wordplay.
'reduced' means to remove the last letter.
'deceit' becomes 'guile' (guile is a kind of deceit).
'over time' becomes 't' (abbreviation. I am not sure about the 'over' bit.).
'guile' with its last letter removed is 'guil'.
'guil'+'t'='GUILT'
Can you help me to learn more?
(Other definitions for guilt that I've seen before include "State of having committed offence" , "(Shame for) criminality" , "Remorse caused by feelings of responsibility" , "Consciousness of one's wrongdoing" , "Sin" .)