20:2. ‘Thousand year(s)’

Greek #5507 chiliŏi ‘plural of uncertain affinity’, ‘thousand’.

Hebrew #505 ’eleph, ‘the first letter of the alphabet, eventually used as the numeral one thousand’.

See also Psalm 68:17.  ‘Thousand years’. BDB p. 1041. ‘Thousands of repetitions, i.e., thousands twice told.’