The inner definition synonyms and antonyms are empty, but the ones outside the definition sometimes have content.
Note there are no entries in the meaning, but entries after the meanings - dunno. Maybe that's just the evolution of the Json layout?

"meanings": [
{
"partOfSpeech": "verb",
"definitions": [
{
"definition": "To disclaim and expel from the family, as a father his child; to disown; to disinherit.",
"synonyms": [],
"antonyms": []
},
{
"definition": "To formally separate oneself from or to divest oneself of.",
"synonyms": [],
"antonyms": []
},
{
"definition": "To depose.",
"synonyms": [],
"antonyms": []
},
{
"definition": "To reject; to cast off; to discard.",
"synonyms": [],
"antonyms": []
},
{
"definition": "To surrender, renounce or relinquish, as sovereign power; to withdraw definitely from filling or exercising, as a high office, station, dignity; to fail to fulfill responsibility for.",
"synonyms": [],
"antonyms": [],
"example": "Note: The word abdicate was held to mean, in the case of James II, to abandon without a formal surrender."
},
{
"definition": "To relinquish or renounce a throne, or other high office or dignity; to renounce sovereignty.",
"synonyms": [],
"antonyms": []
}
],
"synonyms": [
"abandon",
"abjure",
"cast aside",
"cast off",
"cede",
"desert",
"disinherit",
"disown",
"forego",
"forsake",
"give up",
"quit",
"refuse",
"reject",
"relent",
"relinquish",
"renounce",
"repudiate",
"resign",
"retire",
"stand down",
"surrender",
"vacate",
"waive",
"yield"
],
"antonyms": [
"claim",
"grasp",
"maintain",
"occupy",
"retain",
"seize",
"usurp"
]
}