| obligate |
to make someone do something because of a law or moral principle. |
| obligation |
something that someone should or should not do because of a law or moral principle. [2 definitions] |
| oblige |
to make (someone) feel bound to do something or to act in a certain way. [3 definitions] |
| obliging |
ready to help or do favors. |
| oblique angle |
an angle that is not a right angle. |
| oblong |
longer than it is wide. [2 definitions] |
| obnoxious |
offensive or not pleasant. |
| oboe |
a woodwind instrument with a high tone. It has a long, thin body with finger holes or keys, and is played by blowing into a mouthpiece. |
| obscene |
offensive and not decent. |
| obscure |
hard to see or not distinct. [4 definitions] |
| observation |
the act or an instance of perceiving the environment through one of the senses. [3 definitions] |
| observatory |
a building that has equipment for studying the sun, moon, planets, and stars. |
| observe |
to notice or see. [5 definitions] |
| observer |
someone who watches and listens at an event such as a meeting but does not participate in it. |
| obsolete |
no longer in use. |
| obstacle |
something that stops forward movement or progress. |
| obstinate |
not willing to change one's ideas; stubborn. |
| obstruct |
to block or clog. [3 definitions] |
| obstruction |
something that blocks the way or prevents progress. [2 definitions] |
| obtain |
to get; gain. |
| obtuse angle |
an angle greater than 90 degrees and less than 180 degrees. |