How does the prefix 'un-' modify the base word 'healthy'?

The prefix 'un-' when attached to the base word 'healthy' alters its meaning to the opposite. In this case, 'unhealthy' signifies a lack of health or an absence of the qualities associated with being healthy. The prefix 'un-' is commonly used to negate or reverse the meaning of the word it precedes, effectively transforming 'healthy', which suggests well-being and good health, into 'unhealthy', which indicates poor health or undesirable conditions related to health. This process of negation is crucial in understanding how prefixes function in the English language and helps learners expand their vocabulary by recognizing these modifications in meaning.