Irritation overwhelming terribly shy figure (8)
I believe the answer is:
physique
'figure' is the definition.
(synonyms)
'irritation overwhelming terribly shy' is the wordplay.
'irritation' becomes 'pique' (synonyms).
'overwhelming' means one lot of letters goes inside another.
'terribly' indicates anagramming the letters.
'shy' with letters rearranged gives 'hys'.
'pique' placed around 'hys' is 'PHYSIQUE'.
(Other definitions for physique that I've seen before include "Shape and size of a person's body" , "Person's build and muscular development" , "Constitution of the human body" , "Form" , "Bodily type, build, or constitution" .)