English
submillennial
From sub- + millennial.
Formed from sub- + millennial
Proto-Indo-European *upó ‘up; from below’
Proto-Italic *supo ‘under’
Latin sub ‘under, beneath, below’
English sub-
Today it means
adj Pertaining to a time interval less than a thousand years
Language periods are conventional ranges, not dates for this word.
Etymograph / submillennial