What does apply mean?
The definition of apply
Ap*ply”, v. t.
[imp. & p. p. Applied; p. pr. & vb. n. Applying.]
Etym: [OF. aplier, F. appliquer, fr. L. applicare to join, fix, or attach to; ad + plicare to fold, to twist together. See Applicant, Ply.]

1 To lay or place; to put or adjust (one thing to another); — with to; as, to apply the hand to the breast; to apply medicaments to a diseased part of the body. He said, and the sword his throat applied. Dryden.
2 To put to use; to use or employ for a particular purpose, or in a particular case; to appropriate; to devote; as, to apply money to the payment of a debt.
3 To make use of, declare, or pronounce, as suitable, fitting, or relative; as, to apply the testimony to the case; to apply an epithet to a person. Yet God at last To Satan, first in sin, his doom applied. Milton.
4 To fix closely; to engage and employ diligently, or with attention; to attach; to incline. Apply thine heart unto instruction. Prov. xxiii. 12.
5 To direct or address. [R.] Sacred vows . . . applied to grisly Pluto. Pope.
6 To betake; to address; to refer; — used reflexively. I applied myself to him for help. Johnson.
7 To busy; to keep at work; to ply. [Obs.] She was skillful in applying his “humors.” Sir P. Sidney.
8 To visit. [Obs.] And he applied each place so fast. Chapman. Applied chemistry. See under Chemistry.

— Applied mathematics. See under Mathematics.

Ap*ply”, v. i.
1 To suit; to agree; to have some connection, agreement, or analogy; as, this argument applies well to the case.
2 To make request; to have recourse with a view to gain something; to make application. (to); to solicit; as, to apply to a friend for information.
3 To ply; to move. [R.] I heard the sound of an oar applying swiftly through the water. T. Moore.
4 To apply or address one’s self; to give application; to attend closely (to).