re·ac·tant 
(rē-ăktənt)
(rē-ăktənt)n.
A substance that is altered or incorporated into another substance in a chemical reaction, especially a directly reacting substance present at the initiation of the reaction.
- prelusively
- premalignant
- Premarin
- premarital
- premaritally
- premature
- premature atrial contraction
- premature ejaculation
- prematurely
- prematureness
- premature ventricular contraction
- prematurity
- premaxilla
- premaxillary
- premed
- premedical
- premeditate
- premeditation
- premeditative
- premeditator
- premenopausal
- premenstrual
- premenstrual dysphoric disorder
- premenstrually
- premenstrual syndrome