Vine's Expository Dictionary of NT Words 
"safe," is translated "sure" in Hebrews 6:19 . See Certain , B.
"firm, steadfast," is used of (a) God's promise to Abraham, Romans 4:16; (b) the believer's hope, Hebrews 6:19 , "steadfast;" (c) the hope of spiritual leaders regarding the welfare of converts, 2—Corinthians 1:7 , "steadfast;" (d) the glorying of the hope, Hebrews 3:6 , "firm;" (e) the beginning of our confidence, Hebrews 3:14 , RV, "firm" (AV, "steadfast"); (f) the Law given at Sinai, Hebrews 2:2 , "steadfast;" (g) the testament (or covenant) fulfilled after a death, Hebrews 9:17 , "of force;" (h) the calling and election of believers, 2—Peter 1:10 , to be made "sure" by the fulfillment of the injunctions in 2—Peter 1:5-7; (i) the word of prophecy, "made more sure," 2—Peter 1:19 , RV, AV, "a more sure (word of prophecy);" what is meant is not a comparison between the prophecies of the OT and NT, but that the former have been confirmed in the person of Christ ( 2—Peter 1:16-18 ). See Firm.
"faithful," is translated "sure" in Acts 13:34 . See Faithful.
"to make safe or sure" (akin to A, No. 1), is rendered "to make sure" in Matthew 27:64-66 , of the sepulchre of Christ; elsewhere, Acts 16:24 , of making feet fast in the stocks. See Fast.
John 16:30 Romans 2:2 15:29 John 6:69Know.
King James Dictionary 
SURE, a. shure. L. assevero, and to be connected with swear, and perhaps with L. verus s being the remains of a prefix.
1. Certain unfailing infallible.
The testimony of the Lord is sure. Psalms 19
We have also a more sure word of prophecy. 2 Peter 1
2. Certainly knowing, or having full confidence.
We are sure that the judgment of God is according to truth-- Romans 2
Now we are sure that thou knowest all things. John 16 .
3. Certain safe firm permanent.
Thy kingdom shall be sure to thee. Daniel 4
4. Firm stable steady not liable to failure, loss or change as a sure covenant. 2 Samuel 23 . Nehemiah 9; Isaiah 28
The Lord will make my lord a sure house. 1 Samuel 25
So we say, to stand sure, to be sure of foot.
5. Certain of obtaining or of retaining as, to be sure of game to be sure of success to be sure of life or health. 6. Strong secure not liable to be broken or disturbed.
Go your way, make it as sure as ye can. Math 27
7. Certain not liable to failure. The income is sure.
To be sure, or be sure, certainly. Shall you go? be sure I shall.
To make sure, to make certain to secure so that there can be no failure of the purpose or object.
Make sure of Cato.
A peace cannot fail, provided we make sure of Spain.
Give all diligence to make your calling and election sure. 2 Peter 1 .
SURE, adv. Certainly without doubt doubtless.
Sure the queen would wish him still unknown.
But in this sense, surely is more generally used.
Webster's Dictionary 
(1): ( superl.) Certain to find or retain; as, to be sure of game; to be sure of success; to be sure of life or health.
(2): ( superl.) Fit or worthy to be depended on; certain not to fail or disappoint expectation; unfailing; strong; permanent; enduring.
(3): ( superl.) Betrothed; engaged to marry.
(4): ( superl.) Certainly knowing and believing; confident beyond doubt; implicity trusting; unquestioning; positive.
(5): ( superl.) Free from danger; safe; secure.
(6): ( adv.) In a sure manner; safely; certainly.