Cases of word usage

1) (of a committee) to add a person as a member by the votes of those who are already members (coopt)

2) any substance like air (used chiefly of those that are not liquid or solid at ordinary temperatures) (gas)

3) (to threaten) to use force against those in control of (a plane etc) in order to achieve certain aims or to reach a desired destination (hijack)

4) showing colours like those of the rainbow (iridescent)

5) a person who helps those who are poor or in trouble (philanthropist)

6) the mental power by which a person can direct thoughts and actions, and influence those of others; energy, enthusiasm; the control exercised over oneself, one's desires etc; determination; (used as an auxiliary to form the future tense) (will)