Fold up is a commonly used term which refers to the act of folding or doubling something in a neat and organized way. This term can be used to describe various activities such as folding clothes, sheets, blankets, paper, etc. However, there are various synonyms for the word "fold up" which can be used to bring diversity in your vocabulary. Some of the most commonly used synonyms include crumple up, tuck in, roll up, collapse, stack up, compact, pack up, bundle up, etc. These synonyms can be used in various contexts to bring diversity to your writing and make it more interesting and engaging.