To dine before travel shows moral conscience (8)
I believe the answer is:
superego
'moral conscience' is the definition.
(part of the conscience according to Sigmund Freud)
'to dine before travel' is the wordplay.
'to dine' becomes 'sup' ('sup' can be a synonym of 'dine').
'before' becomes 'ere' (poetic term for 'before').
'travel' becomes 'go' (synonyms).
'sup'+'ere'+'go'='SUPEREGO'
'shows' is the link.
(Other definitions for superego that I've seen before include "Moral part of the (Freudian) unconscious" , "makes one feel guilty" , "self-criticism?" , "See group (anag.)" , "self-critic" .)