There are several synonyms for the phrase "in custody," which refers to the state of being held by law enforcement or authorities. One commonly used synonym is "under arrest," indicating that the individual has been detained and is being held for further questioning or legal proceedings. Another similar phrase is "in detention," which implies a temporary confinement for the purposes of investigation or punishment. "Incarcerated" is a more permanent synonym, indicating that the individual has been sentenced and is serving a period of time in a correctional facility. Other synonyms for "in custody" include "in confinement," "in custody of the authorities," and "under the watch of law enforcement".