This term identifies situations in which phonemes are phonologically similar, whether in terms of point of articulation or manner of articulation.
- Nida (1949), a pag.14

Assimilation denotes a process by which phonemes are made similar.
- Nida (1949), a pag.21

There are four factors involved in assimilation and dissimilation: 1. Progressive vs. regressive changes 2. Contiguous vs. noncontiguous phonems 3. Type of articulation 4. Partial vs. complete assimilation.
- Nida (1949), a pag.283

Vowels may assimilate and dissimilate, just as consonants do, but the manner of describing the changes in type of articulation differs. The contrasts in such changes are: high, mid, low; front, central, back; rounded, unrounded; nasal, nonnasal; tense, lax; breathy, nonbreathy; glottalized, nonglottalized, or any other qualitative contrast occurring in the particular language.
- Nida (1949), a pag.287