car·bo·ni·um ion 
(kär-bōnē-əm)
(kär-bōnē-əm)n.
An organic cation, such as H5C+, having a hypervalent carbon atom and a positive charge localized on the carbon atom.
- off the hook
- off-the-rack
- off the rack
- off-the-record
- off the record
- off-the-shelf
- off the shelf
- off the top of head
- off the top of (one's) head
- off the top of one's head
- off the wagon
- off-the-wall
- off the wall
- off the wind
- off-track
- off-track betting
- off-white
- off year
- O'Flaherty
- of late
- ofloxacin
- OFM
- of necessity
- of (one's) word
- of one's word