I believe you're referring to a prefix.
A prefix is a syllable that is added to the beginning of a word to change its meaning or create a new word.
The syllable added to the end of a word is called a suffix. It can modify the meaning or change the grammatical function of the word.
prefix
prefix
prefix
A "prefix". However, note that some prefixes, such as "ante" and "anti", have more than one syllable.
Disastrous has three syllables but, yes, an extra syllable is often added in speech due to the relationship between this word and the word disaster.
prefix
A prefix is a syllable added to the beginning of a word to alter its meaning.
No, adding a syllable to a word typically makes it longer, as more sounds are being added. It is unlikely for a word to become shorter by adding a syllable.
A suffix.
A suffix.