Is tense in formal clothing, producing suffering (8)
I believe the answer is:
distress
'suffering' is the definition.
('distress' can be a synonym of 'suffering')
'is tense in formal clothing' is the wordplay.
'tense' becomes 't' (abbreviation used in many dictionaries).
'in' is an insertion indicator.
'formal' becomes 'dress' ('dress' can be similar in meaning to 'formal'**).
'clothing' indicates putting letters inside.
't' put into 'dress' is 'dtress'.
'is' inserted within 'dtress' is 'DISTRESS'.
'producing' is the link.
(Other definitions for distress that I've seen before include "SOS is such a signal" , "grief" , "Extreme sorrow or pain" , "Anguish - trouble - danger" , "Unhappiness" .)