1. [v]  impregnate, combine, or supply with oxygen; "oxygenate blood"
2. [v]  dehydrogenate with oxygen
3. [v]  change (a compound) by increasing the proportion of the electronegative part; or change (an element or ion) from a lower to a higher positive valence: remove one or more electrons from (an atom, ion, or molecule)

OXYGENISE is a 9 letter word that starts with O.