Part of the week (7)
I believe the answer is:
tuesday
'part of the week' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tuesday that I've seen before include "Ruby - (The Rolling Stones)" , "Shrove ____" , "Part of week (for pancakes?)" , "forty eight hours before Chesterton's man" , "Day the Romans called the day of Mars" .)