late 14c., hyndermest; see hinder (adj.) + -most. Middle English had also hindermore, which, as a noun, could mean "the hinder parts."
Entries linking to hindermost
hinder adj.
"situated in the rear, pertaining to the rear, toward the back," late 14c., probably from an unrecorded Old English adjective from hinder (adv.) "behind, back, afterward," but treated as a comparative of hind (adj.). Related to Old High German hintar, German hinter, Gothic hindar "behind" (prep.).
Middle English had hinderhede, literally "hinder-hood; posterity in time, inferiority in rank;" and hinderling "person fallen from moral or social respectability, wretch," from an Old English term of contempt for a person devoid of honor. Also compare Scottish hinderlins "the buttocks."
-most
superlative suffix of adjectives and adverbs, Middle English alteration (by influence of unrelated most) of Old English -mest, a double superlative, from -mo, -ma (cognate with Latin -mus; compare Old English forma "first," meduma "midmost") + superlative ending -est. Now generally mistaken as a suffixal form of most.