From Tolkien Gateway

Lothron was an Elvish name for the fifth month of the year. Lothron comes from the Sindarin language, and in the Third Age the name was used only by the Dúnedain. Most other calendars in Middle-earth at that time used the Quenya equivalent, which was Lótessë.[1] Both these names come ultimately from the Elvish root-word lot(h), 'flower', and refer to the springtime blossoming associated with this month.