What does reflex mean?
Reflex most commonly denotes an involuntary, automatic response of the body to a stimulus, such as pulling your hand away from a hot surface. By extension, it describes a person's immediate, instinctive reaction: an athlete's first reflex may be to protect the ball. In technical writing, reflex can also relate to a reflex arc, while reflex angle names an angle greater than 180 degrees; the verb reflex is less common and means to bend, turn, or send something sharply backward. The word is neutral in medical and general use, though figurative uses often imply speed, habit, or an unguarded reaction. Reflex comes from Latin reflexus, a form meaning “bent back,” ultimately from re- (“back”) and flectere (“to bend”). The same root underlies reflect and reflection, connecting the physiological sense with the idea of a response traveling back along a nerve pathway and with light sent back from a surface.
An involuntary and relatively automatic response of the body to a stimulus, or an immediate instinctive reaction by a person.
"The bright light triggered a reflex in her eyes."
The figurative sense is common and can suggest a reaction that is quick, habitual, or instinctive.
To bend, turn, or draw sharply backward; to reflect or return.
"The blade struck the guard and reflexed back toward the player."
This use is relatively uncommon and occurs chiefly in technical or descriptive writing.
Relating to an involuntary response; describing something bent or turned back, especially an angle greater than 180 degrees.
"The diagram shows a reflex angle at the vertex of the polygon."
The geometric sense is specialized, while adjectival use in physiology is standard.
The regular plural is used in both medical and figurative contexts.
"The doctor checked the patient's reflexes."
The same Latin root that gives us reflex gives us reflect—and originally meant “to bend backward.”
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does reflex come from?
The English word comes from Latin reflexus, the past participle of reflectere, meaning “to bend back,” which combines re- (“back”) with flectere (“bend”). Latin reflexus was used adjectivally for something bent or turned back, and English developed the physiological noun for an involuntary response transmitted back toward its source. The same Latin root underlies reflect, reflection, reflective, and reflux.
Related word forms
How reflex is actually used
The noun is neutral in medical and general use, while figurative uses often suggest a quick, habitual, or unguarded reaction. Adjectival and verbal uses are uncommon outside specialized contexts.
Easily confused with reflex
A reflex is a response, whereas reflecting is the act of throwing back light, sound, or a thought.
A reflex is an involuntary response, whereas a reflexive action or grammatical form refers back to its subject.