Final answer:
The combining form 'hydr/o' means water.
Step-by-step explanation:
The combining form hydr/o means water. It is derived from the Greek word 'hydr-' which refers to water. This combining form is commonly used in terms related to water or liquid substances, such as hydrate (a compound formed by the addition of water molecules to another substance) and hydrology (the science of water and its distribution on Earth).
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