What does aid mean?
The definition of aid
Aid, v. t.
[imp. & p. p. Aided; p. pr. & vb. n. Aiding.] Etym: [F. aider, OF. aidier, fr. L. adjutare to help, freq. of adjuvare to help; ad + juvare to help. Cf. Adjutant.]

To support, either by furnishing strength or means in coöperation to effect a purpose, or to prevent or to remove evil; to help; to assist. You speedy helpers . . . Appear and aid me in this enterprise. Shak.

— To help; assist; support; sustain; succor; relieve; befriend; coöperate; promote. See Help.

Aid, n.
Etym: [F. aide, OF. aïde, aïe, fr. the verb. See Aid, v. t.]

1 Help; succor; assistance; relief. An unconstitutional mode of obtaining aid. Hallam.
2 The person or thing that promotes or helps in something done; a helper; an assistant. It is not good that man should be alone; let us make unto him an aid like unto himself. Tobit viii. 6.
3 (Eng. Hist.)
A subsidy granted to the king by Parliament; also, an exchequer loan.
4 (Feudal Law)
A pecuniary tribute paid by a vassal to his lord on special occasions. Blackstone.
5 An aid-de-camp, so called by abbreviation; as, a general’s aid. Aid prayer (Law), a proceeding by which a defendant beseeches and claims assistance from some one who has a further or more permanent interest in the matter in suit.

— To pray in aid, to beseech and claim such assistance.