Most peculiar doctor that is retreating in one direction (8)
I believe the answer is:
weirdest
'most peculiar doctor that is retreating in one direction' is the definition.
'weirdest' can be an answer for 'most peculiar' (peculiar can mean weird). I'm not certain of the rest of the definition.
'peculiar doctor that is retreating in one direction' is the wordplay.
'peculiar doctor' becomes 'dr' (abbreviation. I am not sure about the 'peculiar' bit.).
'that is' becomes 'i.e.' (synonyms).
'retreating' is a reversal indicator.
'in' means one lot of letters goes inside another.
'one direction' becomes 'west' (compass direction).
'dr'+'ie'='drie'
'drie' backwards is 'eird'.
'eird' going inside 'west' is 'WEIRDEST'.
Can you help me to learn more?
(Other definitions for weirdest that I've seen before include "Most uncanny!" , "Most bizarre" , "Most strikingly odd" , "Most unearthly" .)