What's the other terms if adults get kidnap?
"Kidnapping" is the name of the crime so you will look to the applicable penal code:
Rhode Island has the following description of "Kidnapping"
Whoever, without lawful authority, forcibly or secretly confines or imprisons another person within this state against his or her will, or forcibly carries or sends another person out of this state, or forcibly seizes or confines or inveigles or kidnaps another person with intent either to cause him or her to be secretly confined or imprisoned within this state against his or her will or to cause him or her to be sent out of this state against his or her will, shall be guilty of a felony and, upon conviction, shall be punished by imprisonment for not more than twenty (20) years.
A separate crime in the state of Rhode Island, "Childsnatching", is described as follows:
(a) Any person who intentionally removes, causes the removal of, or detains any child under the age of eighteen (18) years, whether within or without the state of Rhode Island, with intent to deny another person's right of custody under an existing decree or order of the family court, shall be guilty of a felony, and, upon conviction, shall be punished by imprisonment for a term not more than two (2) years, or a fine of not more than ten thousand dollars ($10,000), or both.
Words tend to change meaning over time, but the word stays the same. Take another example: A "sherriff" in the U.S. is a certain type of law enforcement officer, but not the shire's reeve; we have neither shires nor reeves in the U.S.
Kidnapping has many definitions based on the intent.