The Collaborative International Dictionary of English v.0.48:

Headmost \Head"most`\ (-m[=o]st`), a.
   Most advanced; most forward; as, the headmost ship in a
   fleet.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "headmost":
   acmatic, ahead, antecedent, anterior, apical, arch, banner, before,
   capital, cardinal, central, champion, chief, consummate, crowning,
   dominant, exordial, first, focal, fore, foregoing, forehand,
   foremost, forward, front, frontal, great, head, heading, hegemonic,
   highest, in advance, in front, in the forefront, in the foreground,
   in the front, in the lead, inaugural, initiatory, leading,
   magisterial, main, master, maximal, maximum, meridian, meridional,
   overmost, overruling, paramount, precedent, preceding,
   precessional, precursory, predominant, preeminent, prefatory,
   preliminary, preludial, prelusive, preparatory, preponderant,
   prevailing, prevenient, primal, primary, prime, principal, prior,
   proemial, propaedeutic, ranking, ruling, sovereign, star, stellar,
   summital, supereminent, supreme, tip-top, to the fore,
   to the front, top, topflight, topmost, ultimate, up ahead, upmost,
   uppermost, vertical, zenithal