armgaunt

from The Century Dictionary.

• An epithet of disputed meaning, applied by Shakspere to a horse, and in some editions changed to arrogant.

from the GNU version of the Collaborative International Dictionary of English.

• adjective With gaunt or slender legs. (?)

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective nonce word, obsolete Of uncertain meaning; perhaps describing gaunt or slender legs.