The term 'PERTAINING TO SIGHT' can be summarized by two crossword solutions: OPTICAL (7 letters) and OPTIC (5 letters). OPTICAL is an adjective that means of or relating to sight, vision, or optics. OPTIC is a noun that refers to the eye or vision, or to a device used to magnify or otherwise enhance vision. Both words are related to the field of optics, which is the branch of physics that studies the behavior and properties of light and its interaction with matter.