'Undern' definitions:

Definition of 'Undern'

From: GCIDE

Undern \Un"dern\, n. [AS. undern; akin to OS. undorn, OHG. untarn, untorn, Icel. undorn mid afternoon, mid forenoon, Goth. unda['u]rnimats the midday meal. Cf. Undermeal, Undertime.] The time between; the time between sunrise and noon; specifically, the third hour of the day, or nine o'clock in the morning, according to ancient reckoning; hence, mealtime, because formerly the principal meal was eaten at that hour; also, later, the afternoon; the time between dinner and supper. [Obs. or Prov. Eng.] [1913 Webster]
Betwixt undern and noon was the field all won. --R. of Brunne. [1913 Webster]
In a bed of worts still he lay Till it was past undern of the day. --Chaucer. [1913 Webster]