What is a syllable group of syllables or word joined to the beginning word?

The syllable group of syllables or word joined to the beginning of a word is called a prefix.

Here are some examples:

* un- in unhappy

* re- in rewrite

* pre- in premature

* dis- in disagree

Prefixes can change the meaning of a word. For example, the prefix "un-" means "not," so "unhappy" means "not happy."