late Middle English (in the sense 'attack as a disease'): from French affecter or Latin affect- 'influenced, affected', from the verb afficere (see affect2)
Affect and effect are both verbs and nouns, but only effect is common as a noun, usually meaning ‘a result, consequence, impression, etc.’: my father’s warnings had no effect on my adventurousness. The noun affect is restricted almost entirely to psychology (see affect3). As verbs, they are used differently. Affect most commonly means ‘produce an effect on, influence’: smoking during pregnancy can affect the baby’s development. Affect also means ‘pretend to have or feel (something)’ (see affect2): she affected a concern for those who had lost their jobs. Effect means ‘bring about’: the negotiators effected an agreement despite many difficulties.