With later shortening of the vowel. The indicating "a divide of land" (sense two), attested earlier in watershed (18th century) appears to generally be an outgrowth of earlier Actual physical senses from the phrase, as "the part of one particular's hair" or "a passageway concerning the threads of a warp https://duramax-sheds-for-sale75318.homewikia.com/10754571/duramax_for_dummies