1. a lightweight consumer electronic device that looks like a hand-held computer but instead performs specific tasks
can serve as a diary or a personal database or a telephone or an alarm clock etc.

Synonym: personal digital assistantPDApersonal organizerpersonal organiserorganiser

2. a person who brings order and organization to an enterprise

e.g. she was the organizer of the meeting

Synonym: organiserarranger

3. someone who enlists workers to join a union

Synonym: organiserlabor organizer