Extract from psychotherapist's article (3)
I believe the answer is:
the
'article' is the definition.
(the definite article in English)
'extract from psychotherapist's' is the wordplay.
'extract from' says the answer is hidden in the clue (some letters extracted from the clue).
'THE' is hidden within 'psychotherapists'.
(Other definitions for the that I've seen before include "Base of ever-expanding nursery rhyme" , "Over - - moon" , "SECOND PART OF 23" , "Article is quite definite" , "Last words of story" .)