I think you might mean at the beginning of a word, not a sentence. The only affix that can come at the beginning of a word is called a prefix.
Examples of prefixes:
pre-
re-
bio-
auto-
A prefix is added to the beginning of a word and a suffix is added to the end of one. Example: prefix:dis- suffix:-ing
A prefix, such as "pre" added to "view" to create "preview".
prefix
Suffixes, prefixes and infixes are, each, all parts of a larger group; that of the affixes.
A prefix is a type of affix that attaches to the front of a word.
Suffix is attached in the end. Eg: word "able" which can be added to avoidable, comfortable, etc. Prefix is attached in the beginning. Eg: Dr. for Doctor, ER. for Engineer.
There is another way to describe an affix attached to the beginning of a word. It is typically known as a morpheme.
suffix
A word element attached to a root word that changes its meaning is called an "affix."
Affix, a grammatical element that is combined with a word, stem, or phrase to produce derived and inflected forms. There are three types of affixes: prefixes, unfixes, and suffixes.
which not fixed term....... Affix is a verb it means to attach, stick, join. john affixed a stamp to the letter.
A suffix is attached to the end of a word. A prefix is attached to the beginning of a word.
An affix is a word added to a word to form a new word. For example, 'trans-' is a prefix (type of affix) meaning 'move', or 'change'. An example of a word beginning with 'trans-' is transform, which means to change in shape.
An afformative is another name for an affix - a short portion of a word attached to a stem to form a new word.
I think that the tha antonym of affix is to unfasten, but I am not completely sure....
A prefix, such as "pre" added to "view" to create "preview".
feat is the base word and no affix
A prefix is a type of affix attached to a stem which modifies the meaning of that stem.