The term "naked-eye" refers to observations made by unaided human vision. However, there are several synonyms that can be used to describe this term. One such term is "unaided eye," which refers to the same concept of viewing objects without any assistance from optical instruments. Another word that can be used in place of "naked-eye" is "visually," as it implies that something can be seen or observed with the naked eye. Additionally, the word "unassisted" can be used to describe naked-eye observations, as it refers to the fact that no tools or devices are being used to aid in the observation. Overall, there are several synonyms that can be used in place of "naked-eye" to describe visual observations made without the use of optical instruments.