a bluish translucent magnetic liquid obtained by compressing gaseous oxygen and then cooling it below its boiling point; used as an oxidizer in rocket propellants
a heavy odorless colorless gas formed during respiration and by the decomposition of organic substances; absorbed from the air by plants in photosynthesis
the act of reconnoitring (especially to gain information about an enemy or potential enemy); "an exchange of fire occurred on a reconnaissance mission"