hy·po·pla·sia 
(hī′pō-plāzhə)
(hī′pō-plāzhə)n.
Incomplete or arrested development of an organ or a part.
hy′po·plastic (-plăstĭk) adj.
- 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
- on pins and needles
- on principle
- on purpose
- on radar screen
- on radar screen
- on record
- on relief
- on report
- on request
- onrush
- onrushing
- Onsager
- on sale
- onscreen