ar·chen·ter·on 
(är-kĕntə-rŏn′, -tər-ən)
(är-kĕntə-rŏn′, -tər-ən)n.
The central cavity of the gastrula, which ultimately becomes the intestinal or digestive cavity.
ar′chen·teric (är′kĕn-tĕrĭk) adj.
- on one's own hook
- on (one's) own initiative
- on one's own initiative
- on (one's) radar/radar screen
- on one's radar screen
- on one's radar screen
- on (one's) soapbox
- on one's soapbox
- on (one's)/the way
- on (one's) /the way
- on one's the way
- on (one's) toes
- on one's toes
- on (one's) uppers
- on one's uppers
- on one's way
- on one/the onehand
- on order
- on own
- on own account
- on own ground
- on own hook
- on own initiative
- on pain of
- on paper