Meaning of REFLEX in English

REFLEX

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.