The name of the day that came fifth in the week according to usage in the Shire at the end of the Third Age. Also called 'Hensday', it fell between Trewsday and Mersday, and can be considered (at least phonetically) equivalent to modern 'Wednesday'.
The day's name means 'Heavens' Day', from an earlier form Hevenesdei which itself was adapted from the Númenóreans, and ultimately from the Elves. In Númenor, Elvish was used to name the days, and so the fifth day of the week was originally known by its Quenya name, Menelya.