The Collaborative International Dictionary of English v.0.48:

Morn \Morn\ (m[^o]rn), n. [OE. morwen, morgen, AS. morgen; akin
   to D. morgen, OS. morgan, G. morgen, Icel. morginn, morgunn,
   Sw. morgon, Dan. morgen, Goth. ma['u]rgins. Cf. Morrow,
   Morning.]
   The first part of the day; the morning; -- used chiefly in
   poetry.
   [1913 Webster]

         From morn
         To noon he fell, from noon to dewy eve.  --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

morn
    n 1: the time period between dawn and noon; "I spent the morning
         running errands" [syn: morning, morn, morning time,
         forenoon]

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "morn":
   AM, Ack Emma, ante meridiem, aurora, cockcrow, dawning, daybreak,
   daylight, foreday, forenoon, grey-eyed morn,
   incense-breathing morn, light, matins, morning, morning time,
   morntime, sunrise, sunup, this AM, this morning, waking time