Clue: Whereby patient session starts with therapist's bottom in designer chair amid wise pronouncement (10)
Answer: PSYCHIATRY
Explanation: Whereby patient session starts with therapist's bottom in designer chair amid wise pronouncement (10)
A charade of PS ('**P**atient **S**ession starts') plus a double envelope ('in' and 'amid') of T ('therapis**T**'s bottom') in CHIAR, an anagram ('designer') of 'chair' in YY ('wise pronouncement' i.e. 'wise' soudns like Ys), with a somewhat jaundiced extended definition.