The word 'unsanitary' is a modern English formation built upon the established adjective 'sanitary'. The core concept of health, 'sanitas', originates from the Latin adjective sanus meaning 'healthy, sound'. The negative prefix 'un-', with deep roots in Proto-Germanic and Old English, is systematically attached to adjectives to indicate the opposite quality. Therefore, the literal construction "not healthy/clean" directly and logically yields the modern meaning describing conditions that are unclean and conducive to disease.

Structure: un (not) + sanitary (clean) - un: A prefix of Germanic origin (Old English un-), used to form words expressing negation or absence. - sanitary: An adjective of Latin origin (from Latin sanitas meaning 'health'), describing conditions relating to health and cleanliness.