What is the difference between aid and aide?

[Macy]

English Language Tests, Intermediate level

ESL/EFL Test #220 "Confusing Words test (3)", question 7

Thomas really likes the nursing home his children chose for him because his personal ......... is nice and competent.

(a) aids
(b) aid
(c) aide
(d) add

English Language Tests, Intermediate level

ESL/EFL Test #220 "Confusing Words test (3)", answer 7

Thomas really likes the nursing home his children chose for him because his personal aide is nice and competent.

Correct answer: (c) aide

Your answer was: incorrect
Thomas really likes the nursing home his children chose for him because his personal aid is nice and competent.
_________________________

What means aide? Aid is a purpose... I can't understand whole meaning of this sentence.

Macy

[Diverhank]

Aide is a person who helps you