Reduplication in Ngiyambaa is used to reduce specificity of the reference of a word and make it vaguer (Donaldson 1980: 70). (We can label this 'attenuative', though Donaldson does not use the term.) Though clearly not an inflectional category, it is nonetheless highly regular; in particular, the majority of verbs can be reduplicated, except where this is semantically excluded, i.e. events which cannot occur 'more-or-less' (p. 75). In this context, the existence of a small set of verbs where there is a morphological restriction on reduplication can be seen as a marginal instance of defectiveness.
Reduplication involves the repetition of the first syllable and the first CV of the second syllable:
dhala~dhalarbi-ya ATT~shiny-PRS 'is pretty shiny'
Naturally, such a template presupposes that the verb has at least two syllables. Donaldson writes 'It proved impossible to elicit reduplicated forms of any monosyllabic verb roots...' (p. 197).1 Instead, an alternative strategy is employed involving a compound construction with the verb (or verbal prefix) bala- 'using little energy'. For example, with the verb ŋa:-y 'see':
unattested reduplication attested compound *ŋa~ŋa-nhi=dju=na balamiyi=dju=na ŋa-nhi ATT~see-PST=1.NOM=3.ABS do.unenergetically=1.NOM=3.ABS see-PST 'I more or less looked at it.' 'I looked at it unergetically.'
1 Out of 270 monomorphemic verbs, 9 are monosyllabic. Nonmonomorphemic verbs are compounds.
Donaldson, Tamsin. 1980. Ngiyambaa: the language of the Wangaaybuwan. Cambridge: Cambridge University Press.