1. Not accessible to direct observation

See also: imperceptible, unperceivable

• isocline
• isoclinic
• isoclinic line
• Isocrates
• isocurvature
• isocyanate
• isocyanic acid
• isocyclic
• isodiametric
• isodynamic
• isoelectronic
• Isoetaceae
• Isoetales
• Isoetes
• isoflurane
• isogamete
• isogamy
• isogloss
• isogon
• isogonal line
• isogone
• isogonic
• isogonic line
• isogram
• isohel