A mora is a unit of organisation used in phonology as a way to explain how segments such as [h] or [o] appear in a sequence, relate to one another or are subject to phonological rules such as stressing. As a unit of prosody, it is similar to the syllable but languages vary in how moras are employed, if at all. For example, in Japanese, moras define how long a syllable or other unit is relative to others: the single syllable hon 'book' is underlain by two moras, one for ho and one for n, and these are roughly similar in duration. The Japanese kana writing system represents moras rather than syllables, so hon is written with two symbols: ほん.
In English, moras do not control duration of segments or syllables but instead influence which syllable is stressed: a syllable containing two moras in its rhyme (the part after the initial consonant-bearing onset), and therefore at least two segments, is 'heavy' and so likely to 'attract' stress. A 'light' syllable, which contains only one mora in its rhyme and therefore only one segment, is 'light' and so less likely to be stress-bearing in a multisyllabic utterance. Final syllables, however, are often ignored. For example, in the word romantic [ɹə.mæn.tɪk] the first non-final heavy syllable from the right receives main stress, i.e. [-mæn-]. [ɹə-], despite being the first syllable in the word, has only one mora in its rhyme and so is not stressed.
- Often pluralised as morae.