1) of two or more things that may be used, chosen etc in place of the other or others (alternative)

2) a pen with a small ball in place of a nib which rolls ink onto paper (ballpoint)

3) a bed quilt (filled with leathers or an artificial substitute) used in place of blankets (duvet)

4) (an instance of) the use of less exact but less harsh words or phrases in place of words required by truth or accuracy (euphemism)

5) (in stories) a woman with a fish's tail in place of legs (mermaid)

6) not at any time; not at any time up to the present; (used for emphasis in place of 'not') (never)