Meaning of REFLEX in English
re ‧ flex /ˈriːfleks/ BrE AmE noun [countable]
[ Date: 1500-1600 ; Language: Latin ; Origin: past participle of reflectere ; ⇨ ↑ reflect ]
1 . reflexes [plural]
a) the natural ability to react quickly and well to sudden situations
have good/quick/slow reflexes
A tennis player needs to have very quick reflexes.
b) a sudden uncontrolled movement that your muscles make as a natural reaction to a physical effect:
Doctor Mulholland tested Jennifer’s reflexes (=especially by hitting her knee with a special rubber hammer) .
2 . reflex action something that you do without thinking, as a reaction to a situation
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012