Sentence:  - Syllables are linguistic units centering in peaks which <WSD>are</WSD> usually vocalic but , as has been noted , are consonantal under certain circumstances , and which may or may not be combined with preceding and / or following consonants or combinations of consonants . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)