__ Tuesday (4)
(Other definitions for taco that I've seen before include "Mexican food" , "Mexican dish of rolled tortilla with filling" , "Set of three" , "Mexican rolled pancake with a filling" , "Coat with Mexican dish" .)
'tuesday' is the definition.
(I have seen 'a Tuesday' mean 'shrove' so perhaps 'tuesday' could also mean 'shrove')
This is all the clue.
(Other definitions for shrove that I've seen before include "Heard confession" , "This Tuesday comes before Ash Wednesday" , "... Tuesday precedes Ash Wednesday" , "This Tuesday is immediately before Ash Wednesday" , "The Tuesday before Lent" .)
(Another definition for til that I've seen is " Sesame".)