"Tightened up" is a phrase that signifies the act of making something more secure, compact, or restricted. There are many synonyms for this phrase that can be used to convey the same meaning such as constricted, compressed, condensed, contracted, immured, restrained, confined, hardened, and tautened. Each of these words carries a different connotation and they can be used to suit the context in which they are employed. For instance, if you want to express that a person has become more reserved, restrained could be used. If you want to signify that something has become more rigid, hardened can be used. The right synonym for "tightened up" can make all the difference in the way you express yourself.