Source: A 1931 dictionary
Du'i cirā (दुइ चिरा) literally means "two splits". It is the proper Nepali spelling for what is known among collectors as dui chirra, a name for a khukuri that has two broad fullers in the blade. Each cirā, then, refers not to the fuller itself but to the sharp ridge created between them.
According to Taylor, cirā is derived of cirnu, literally "To split, rip up, cut, lacerate". It is also used in the slightly different form, ciro (चिरो) to describe: "A splinter; cut, slice; (esp.) a slice of cucumber cut lengthwise." 1
A classic du'i cirā (दुइ चिरा) khukurī.
Sub-types of groove layouts
Among antiques, we typically encounter four main types of blade:
Āṅa (आङ); flat, like a kitchen knife.2
Āṅa khol (खोल् आङ); a single fuller running along the spine. (Commonly called ang khola.)
Du'i cirnu (दुइ चिर्नु); "two split", two fullers in the blade. (Commonly called dui chirra.)
Tīna cirnu (तीन चिर्नु); "three split", three fullers in the blade. (Commonly called tin chirra.)
Also see: A Nepalese khukurī glossary
1. Sir Ralph Lilley Turner; A comparative and etymological dictionary of the Nepali language. London: K. Paul, Trench, Trubner, 1931.
2. Resham Shercha, an ex Ghurka. Personal communication.