It's possible to sit in the dentist's chair (3)
I believe the answer is:
tis
'it's possible to sit' is the definition.
I can't tell whether this defines the answer.
'in the dentist's chair' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TIS' is hidden within 'dentists chair'.
Can you help me to learn more?
(Other definitions for tis that I've seen before include "Contraction of it is" , "For poet, that's" , "Sequel to "Angela's Ashes"" , "Pacific trees" , "It is shortened" .)