Which combining form indicates sensation or feeling?

The combining form that indicates sensation or feeling is "esthesi/o." This term is derived from the Greek word "aisthesis," which means sensation or perception. It is commonly used in medical terminology to refer to the different types of sensations, including touch, temperature, and pain. Terms such as "anesthesia" (loss of sensation) and "hyperesthesia" (increased sensitivity to stimulation) utilize this combining form to convey concepts related to feeling and sensation.

The other combining forms provided relate to different anatomical or physiological structures: "fibr/o" refers to fibrous tissue, "erythr/o" pertains to red blood cells or the color red, and "femor/o" relates to the femur or thigh bone. Each of these forms serves a specific purpose in the medical lexicon but does not connect to the concept of sensation or feeling like "esthesi/o" does.