In a jittery state, go as fire's spread (4,4)
I believe the answer is:
foie gras
'spread' is the definition.
(I know that foie gras is a type of pt)
'in a jittery state go as fire's' is the wordplay.
'in a jittery state' indicates anagramming the letters (letters become jittery or excited).
'go'+'as'+'fire'='goasfire'
'goasfire' anagrammed gives 'FOIE GRAS'.
(Other definitions for foie gras that I've seen before include "Pate de . . . . . . . . Is made from goose liver" , "Pate made from liver of fatted goose" , "P?t? from goose livers" , "Edward ---, discovered vaccination" , "French delicacy" .)