There are a number of synonyms for the phrase "be delinquent." Some common alternatives include "fall behind," "default," "neglect," "overdue," "in arrears," "unpaid," and "past due." In each case, the underlying meaning is the same: failing to meet an obligation or responsibility on time. This can refer to a variety of situations, such as failing to pay bills, returning library books late, or missing deadlines for work or school. Whatever the context, being delinquent is generally seen as a negative thing, since it suggests a failure to meet expectations or responsibilities. As such, it is important to stay on top of one's obligations and avoid falling behind or becoming delinquent.