Anapest is antidactylus because it is the reverse of dactyl. What is dactyl? Refer to O's earlier commentary on dactyl, or let us simply continue, but bearing in mind that dactyl is the reverse of anapest.
Anapest is a three-syllabic foot in a verse where two unstressed syllables are followed by one stressed syllable.
Lord Byron's poem The Destruction of Sennacherib is a good example of a poem written in anapestic meter.
The Assyrian came down like the wolf on the fold,
And his cohorts were gleaming in purple and gold
And the sheen of their spears was like stars on the sea,
When the blue wave rolls nightly on deep Galilee
The Assyr | ian came down | like the wolf | on the fold
And his co | horts were gleam | ing in purp | le and gold
And the sheen | of their spears | was like stars | on the sea
When the blue | wave rolls night | ly on deep | Galilee
This poem is written in anapestic tetrameter.