The term phonestheme (or phonaestheme in British English) was coined in 1930 by British linguist J. R. Firth (from the Greek φωνή phone, "sound", and αἴσθημα aisthema, "perception" from αίσθάνομαι aisthanomai, "I perceive") to label the systematic pairing of form and meaning in a language. Such pairing would violate the arbitrariness principle of semantics.
Phonesthemes are of critical interest to students of the internal structure of words because they appear to be a case where the internal structure of the word is non-compositional; i.e., a word with a phonestheme in it has other material in it that is not itself a morpheme. Phonesthemes "fascinate some linguists," as Ben Zimmer has phrased it, in a process that can become "mystical" or "unscientific."
For example, the English phonestheme "gl-" occurs in a large number of words relating to light or vision, like "glitter", "glisten", "glow", "gleam", "glare", "glint", and so on; yet, despite this, the remainder of each word is not itself a phonestheme (i.e., a pairing of form and meaning); i.e., "-isten", "-ow", and "eam" do not make meaningful contributions to "glisten", "glow", and "gleam". There are three main ways in which phonesthemes are empirically identified.
The first is through corpus studies, where the words of a language are subjected to statistical analysis, and the particular form-meaning pairing, or phonestheme, is shown to constitute a statistically unexpected distribution in the lexicon or not.
Corpus studies can inform a researcher about the current state of the lexicon, a critical first step, but importantly are completely uninformative when it comes to questions of whether and how phonesthemes are represented in the minds of language users.
Study of patterns in neologisms
The second type of approach makes use of the tendency for phonesthemes to participate in the coinage and interpretation of neologisms, new words in a language. Various studies have demonstrated that when asked to invent or interpret new words, subjects tend to follow patterns predicted by looking at the phonesthemes in their language. This approach demonstrates the vitality of phonesthemic patterns, but still does not provide any evidence about whether or how phonesthemes are represented in the minds of speaker-hearers.
Study of linguistic processing patterns
The final type of evidence uses the methods of psycholinguistics to study exactly how phonesthemes participate in language processing. One such method is phonesthemic priming, akin to morphological priming, which demonstrates that people represent phonesthemes much as they do typical morphemes, despite the fact that phonesthemes are non-compositional.
Discussions of phonesthesia are often grouped with other phenomena under the rubric of sound symbolism.
While phonesthemes have mostly been identified in the onsets of words and syllables, they can have other forms. There has been some argument that sequences like "-ash" and "-ack" in English also serve as phonesthemes, due to their patterning in words that denote forceful, destructive contact ("smash", "crash", "bash", etc.) and abrupt contact ("smack", "whack", "crack", etc.), respectively.
In addition to the distribution of phonesthemes, linguists consider their motivation. In some cases, there may appear to be good sound-symbolic reasons why phonesthemes would have the form they have. In the case of "-ack", for example, we might imagine that the words sharing this phonestheme do so because they denote events that would produce a similar sound. But critically, there are many phonesthemes for which there can be no sound-symbolic basis, such as "gl-", for the simple reason that their meanings (such as 'pertaining to light or vision') entail no sound.
Examples of phonesthemes in English (i.e., aside from "gl-"), include "sn-", related to the mouth or nose, as in "snarl", "snout", "snicker", "snack", and so on; and there is also a set of words starting with "sl-", which appears in words denoting frictionless motion, like "slide", "slick", "sled", and so on - which are themselves a subset of a larger set of words beginning with sl- that are pejorative behaviours, traits, or events: slack, slouch, sludge, slime, slosh, slash, sloppy, slug, sluggard, slattern, slut, slang, sly, slither, slow, sloth, sleepy, sleet, slip, slipshod, slope, slit, slay, sleek, slant, slovenly, slab, slap, slough, slum, slump, slobber, slaver, slur, slog, slate.
A further phonesthetic phenomenon, ablaut phonesthesia, mimics the paradigm of a strong verb like swim : swam : swum with internal vowel change or apophony. Take the word "flip." It has an alliterative group, "fl-", that evokes the volatility of fly, flow, flee, fleet, flash, flake, and flick. Its rhymes, dip, sip, quip, drip, pip, tip, slip, and so forth, add to a connotation of minor labile action. But it is also part of an ablaut series where vowel alternation has semantic value (as in "flip-flop").
This kind of vowel alternation can be found in reduplicated word pairs like "pitter-patter," "chit-chat," "tip-top," or "tip-tap." The series flip : flap : flop : flub has the same vowels as sing : sang : song : sung.
Another such series is drip : drop : droop : drape. A regularity of phonesthetic relationship is shown by proportional analogies such as clip : clasp :: grip : grasp or crash : crush :: mash : mush or crash : crunch :: mash : munch.
- Marchand, Hans (1959), "Phonetic Symbolism in English Word-Formation", Indogermanische Forschungen, Volume 64, pp.146-168, 256-277 , 
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