The Proto-Indo-European system of root vowel alternations. There existed the following variants or "grades" of ablaut: full (or "e") grade, full grade with ablaut (or "o"), lengthened grade, lengthened grade with ablaut, and zero grade. The results of this alternation can be seen in the following ModE related words (listed in the same order as the above grades): sit, sat, seat, soot, nest; and also in the English strong verb system.

The bound morpheme used to indicate the grammatical function of a word. e.g., -'s to indicate the possessive as in boy's, or -s or -es to indicate the plural.

The smallest unit of meaning. Any word or part of a word that conveys meaning and cannot be further divided into smaller meaningful elements.

Words that through their segments imitate sounds one can hear in the environment. e.g., whoosh, meow, clink, bong, boom, creak, cockadoodledoo, cheep, zoom, buzz, etc.

A branch of linguistics dealing with the analysis, description, and classification of speech sounds, or segments.

The simplest significant unit of sound. A phoneme may also have various allophones.

The assimilation - through fronting, backing, raising, or lowering - of a class of vowels to a set of segments in an immediately neighboring syllable. e.g., PGmc. *fulljan- > OE fyllan 'fill', PGmc. *gulda > OE gold, OHG furi > NHG für 'for'.

A word formed by combining the initial letters of a series of related words. e.g., radar, Nato, snafu, etc.

Any segment produced by stopping and releasing the air stream (stops), or stopping it at one point while it escapes at another (liquids), or a very narrow passage causing friction (fricatives).

The process by which a sound becomes dissimilar to another sound. e.g., Lat. turtur > Mod E. turtle, Lat. marmor > ModE marble.

The addition of a vowel to break up perceived difficult consonant clusters. e.g., Lat. faclis > facilis; ModE athlete > variant 'athelete'.

This occurs when the belief exists that saying a certain word is unacceptable, either 1) because it might evoke that thing, 2) it might be considered too sacred, or 3) perhaps it is too profane. A euphemism develops so that the thing can be talked about without actually saying it. e.g., 1) Eng. bear <'the brown one' replacing the original, now lost, word probably a cognate of Grk. arktos; 2) Hebr. adonai; 3) gosh, heck or darn for certain well-known profane words.

A consonant produced when the air released by an articulator passes through a narrow passage with audible friction. e.g., , , [þ], [ð], etc.