From head +‎ -most.

headmost (not comparable)

1. Closest to the front of a group or pack
   • 1836, Richard Henry Dana, Two Years Before the Mast‎^[1]:

     The headmost was a ship, and the other, a brig.

   • 1859, Sir Walter Scott, “Rob Roy”, in Arthur Mee and J.A. Hammerton, Eds., editor, The World's Greatest Books, Vol VIII‎^[2]:

     The headmost hounds soon burst out of the coppice, followed by three or four riders with reckless haste, regardless of the broken and difficult nature of the ground. "

   • 1914, Ernest Scott, The Life of Captain Matthew Flinders‎^[3]:

     We were now the headmost line of battle ship and gaining fast upon the enemy; but the main part of our fleet seemed rather to drop from them.

• hatedoms