1. To fasten, join, or attach (usually followed by "to"): Mary affixed postage stamps to the envelopes that she was going to mail to her friends.
2. To put or to add on; to append: The salesman wanted Alice to affix her signature to the contract for the loan.

In grammar, a part of a word element that is affixed, such as a prefix, infix, or suffix, is added to a word element in order to form a different meaning. For example, the suffix, "-ed" added to "want" forms "wanted", or the prefix, "im-" connected to "possible" becomes "impossible".

When a poster is affixed to the wall, it is secured or tacked to the wall.