"the very thing," early 13c., from þe "the" (see the) + ilce "same" (see ilk).
"Plym" is the swelling of wood when it is immersed in water; and "thilk," another Anglo-Saxon word, means thus or the same.
J. Arthur Gibbs
This is thilk disciple that bereth witnessyng of these thingis, and wroot them.
Robert Gordon Latham