Approximants are speech sounds that involve the articulators approaching each other but not narrowly enough nor with enough articulatory precision to create turbulent airflow. Therefore, approximants fall between fricatives, which do produce a turbulent airstream, and vowels, which produce no turbulence. This class is composed of sounds like (as in rest) and semivowels like and (as in yes and west, respectively), as well as lateral approximants like (as in less). Terminology Before Peter Ladefoged coined the term "approximant" in the 1960s, the terms "frictionless continuant" and "semivowel" were used to refer to non-lateral approximants. In phonology, "approximant" is also a distinctive feature that encompasses all sonorants except nasals, including vowels, taps and trills. Semivowels Some approximants resemble vowels in acoustic and articulatory properties and the terms semivowel and glide are often used for these non-syllabic vowel-like segments. The correlation between semivowels and vowels is strong enough that cross-language differences between semivowels correspond with the differences between their related vowels. Vowels and their corresponding semivowels alternate in many languages depending on the phonological environment, or for grammatical reasons, as is the case with Indo-European ablaut. Similarly, languages often avoid configurations where a semivowel precedes its corresponding vowel. A number of phoneticians distinguish between semivowels and approximants by their location in a syllable. Although he uses the terms interchangeably, remarks that, for example, the final glides of English par and buy differ from French par ('through') and baille ('tub') in that, in the latter pair, the approximants appear in the syllable coda, whereas, in the former, they appear in the syllable nucleus. This means that opaque (if not minimal) contrasts can occur in languages like Italian (with the i-like sound of piede 'foot', appearing in the nucleus: , and that of piano 'plan', appearing in the syllable onset: ) and Spanish (with a near minimal pair being abyecto 'abject' and abierto 'opened'). {|class="wikitable" |- |+Approximant-vowel correspondences ! Vowel ! Correspondingapproximant ! Place of articulation ! Example |- | || ** || Palatal || Spanish amplío ('I extend') vs. amplió ('he extended') |- | || || Labiopalatal || French aigu ('sharp') vs. aiguille ('needle') |- | || ** || Velar || |- | || || Labiovelar || Spanish continúo ('I continue') vs. continuó ('he continued') |- | || || Pharyngeal || |- | || || Postalveolar, retroflex ||North American English waiter vs. waitress |} Because of the articulatory complexities of the American English