(n.) The euphonic modification of a root vowel sound by the influence of a, u, or especially i, in the syllable which formerly followed.

Indian file ablaut acoustic phonetics array articulation articulatory phonetics assortment bank betacism buzz categorization catena catenation chain chain reaction chaining change concatenation connection consecution continuity continuum course culling cycle degree descent difference distinction divergence drone endless belt endless round file filiation gamut grading graduation grouping hierarchy hum line lineage modification monotone morphophonemics mutation nexus nuance orthoepy pendulum periodicity phonetics phonology place placement plenum powder train progression queue range rank ranking recurrence reticulation rhotacism rotation round routine row run scale screening selection sequence serial order series shade shading sifting single file sorting sorting out sound shift spectrum string subordination succession swath taxonomy thread tier train triage umlaut variation windrow