Bitterly discontented, try to get bit of TLC off Pat (2,5)
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I believe the answer is:
by heart
'off pat' is the definition.
(I've seen this before)
'bitterly discontented try to get bit of tlc' is the wordplay.
'discontented' suggests removing the centre (the word's contents are removed).
'try' becomes 'hear' (as in to try someone in court or hear their case).
'to get bit of' suggests taking the first letters (just the first 'bit').
'bitterly' with its middle removed is 'by'.
The initial letter of 'tlc' is 't'.
'by'+'hear'+'t'='BY HEART'
(Other definitions for by heart that I've seen before include "To know - - is to have in the memory" , "One way to remember" , "how circulation is maintained" , "Off pat" , "Thoroughly memorized, word perfect" .)