With afterwards shortening from the vowel. The that means "a divide of land" (perception 2), attested before in watershed (18th century) seems for being an outgrowth of before Actual physical senses in the term, as "the part of one particular's hair" or "a passageway between the threads of a warp https://knoxdimps.plpwiki.com/6104580/the_5_second_trick_for_sheds