Plant hormone is a term used to describe the various chemicals produced within plants that control their growth, development, and responses to external stimuli. These hormones play a crucial role in regulating plant growth, apoptosis, and reproductive processes. There are several synonyms for the term 'plant hormone,' and they include phytohormone, plant growth substance, plant growth regulator, and plant growth hormone. Phytohormone is the most commonly used synonym and refers to any plant-derived substance that regulates plant growth. Plant growth substance and regulator support the same meaning, while plant growth hormone specifically describes hormones that stimulate the growth of a plant. Overall, these synonyms describe the various chemicals used by plants to regulate their growth and development.