from
The Collaborative International Dictionary of English v.0.48
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]