tonologically

[T]he fact that a lexically specifiable subgroup of etyma from within the whole group of *creaky phonation etyma split off tonologically is not surprising by itself, but rather the fact that the tonological outcome of such a development is one of blurred and opaque relationships within the resulting tone pattern.

1987, Alfons Weidert, “Evidence for PTB *Creaky Phonation = T/G/Th *A-tone”, in Tibeto-Burman Tonology: A Comparative Account (Amsterdam Studies in the Theory and History of Linguistic Science. Series IV, Current Issues in Linguistic Theory; 54), Amsterdam; Philadelphia, Pa.: John Benjamins Publishing Company, →ISBN, page 303

In some cases, tenses keep this tone contrast, in others these tones are neutralized by either assigning tones to non-toned verb stems or by deleting tones, making all types of verb stems look the same tonologically speaking.

Morphology: An International Handbook on Inflection and Word-Formation

2004, Alexandre Kimenyi, “Kinyarwanda (Bantu)”, in Geert [E.] Booij, Christian Lehmann, Joachim Mugdan, Stavros Skopeteas, editors, Morphologie: Ein Internationales Handbuch Zur Flexion und Wortbildung [Morphology: An International Handbook on Inflection and Word-Formation], volume 2, Berlin; New York, N.Y.: Walter de Gruyter, →ISBN, page 1533

Derivative suffixes marked by an asterisk are tonologically flexible; they do not take a fixed tone but rather vary in their tonal behaviour in accordance with the tonal pattern of the verb stem.

2013, “Morphology”, in Rainer Vossen, editor, The Khoesan Languages (Routledge Language Family Series), Abingdon, Oxon.; New York, N.Y.: Routledge, →ISBN, page 212