Dictionary.net

• Said of an irregular, monopetalous corolla, the lower being three-lobed.

1914 - Nuttall's Standard dictionary of the English language
By Nuttall, P.Austin.

• Formed with lips; in bot., applied to irregular gamopetalous flowers with an upper and under portion separated more or less by a hiatus or gap.

1874 - Etymological and pronouncing dictionary of the English language
By Stormonth, James, Phelp, P. H.