The name used in the Shire and the Bree-land, at the time of the of the War of the Ring, for the fifth month of the year, following Astron and preceding Forelithe on the Shire Calendar. It corresponded to the months of Lótessë and Lothron in the calendars of Men, and approximately to modern May (Thrimidge would run from 22 April to 21 May on a Gregorian calendar).
In older times the name of this month had been Thrimilch (from Old English þri-milce, 'three milkings'), and even at the end of the Third Age the name was sometimes spelt 'Thrimich' rather than 'Thrimidge', a form that reflected the word's origins.
Notes
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This month's name ultimately derives from Old English þri-milce. At this time of the year cows would need to be milked three times each day (a fact important enough in an agricultural community to be used as the name of a month).