Wiktionary
underlying form
n. (context phonology English) A property of a morpheme; the abstract form that the morpheme is postulated to have before any phonological rules have applied to it.
Usage examples of "underlying form".
A confused mass of detail could not be held in the memory, the underlying form could not be abstracted from raw sense impressions.
When the cap was in place, Eric began sewing, pinching the blanket material and stitching lengths of it together in ridges up and down the shaft, bringing it tight against the underlying form.