Boyd’s Bible Dictionary:

Punishment of theft was severe under the Mosaic law, as in all pastoral countries where the property was chiefly in flocks, more or less exposed to persons of felonious intent

Concise Bible Dictionary:

1. ληστής “robber, bandit.” Used by the Lord in reference to those who bought and sold in the temple (Matt. 21:1313And said unto them, It is written, My house shall be called the house of prayer; but ye have made it a den of thieves. (Matthew 21:13); Mark 11:1717And he taught, saying unto them, Is it not written, My house shall be called of all nations the house of prayer? but ye have made it a den of thieves. (Mark 11:17); Luke 19:4646Saying unto them, It is written, My house is the house of prayer: but ye have made it a den of thieves. (Luke 19:46)). In the parable of the Good Samaritan the traveler fell among robbers (Luke 10:30, 3630And Jesus answering said, A certain man went down from Jerusalem to Jericho, and fell among thieves, which stripped him of his raiment, and wounded him, and departed, leaving him half dead. (Luke 10:30)
36Which now of these three, thinkest thou, was neighbor unto him that fell among the thieves? (Luke 10:36)
). When the Lord was arrested He asked if they had come out as against a robber (Matt. 26:5555In that same hour said Jesus to the multitudes, Are ye come out as against a thief with swords and staves for to take me? I sat daily with you teaching in the temple, and ye laid no hold on me. (Matthew 26:55); Mark 14:4848And Jesus answered and said unto them, Are ye come out, as against a thief, with swords and with staves to take me? (Mark 14:48); Luke 22:5252Then Jesus said unto the chief priests, and captains of the temple, and the elders, which were come to him, Be ye come out, as against a thief, with swords and staves? (Luke 22:52)). The two malefactors crucified with the Lord were also men of this character (Matt. 27:38,4438Then were there two thieves crucified with him, one on the right hand, and another on the left. (Matthew 27:38)
44The thieves also, which were crucified with him, cast the same in his teeth. (Matthew 27:44)
; Mark 15:2727And with him they crucify two thieves; the one on his right hand, and the other on his left. (Mark 15:27)). The same Greek word is translated “robber” in the AV in John 10:1, 81Verily, verily, I say unto you, He that entereth not by the door into the sheepfold, but climbeth up some other way, the same is a thief and a robber. (John 10:1)
8All that ever came before me are thieves and robbers: but the sheep did not hear them. (John 10:8)
; John 18:4040Then cried they all again, saying, Not this man, but Barabbas. Now Barabbas was a robber. (John 18:40); and 2 Cor. 11:2626In journeyings often, in perils of waters, in perils of robbers, in perils by mine own countrymen, in perils by the heathen, in perils in the city, in perils in the wilderness, in perils in the sea, in perils among false brethren; (2 Corinthians 11:26).
2. κλέπτης, “thief.” Those who break through and steal secretly (Matt. 6:19-2019Lay not up for yourselves treasures upon earth, where moth and rust doth corrupt, and where thieves break through and steal: 20But lay up for yourselves treasures in heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal: (Matthew 6:19‑20)). This is the word employed in the expression “as a thief in the night,” to which the unexpected coming of the Lord to the world is compared (1 Thess. 5:2,42For yourselves know perfectly that the day of the Lord so cometh as a thief in the night. (1 Thessalonians 5:2)
4But ye, brethren, are not in darkness, that that day should overtake you as a thief. (1 Thessalonians 5:4)
; 2 Pet. 3:1010But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up. (2 Peter 3:10); Rev. 3:33Remember therefore how thou hast received and heard, and hold fast, and repent. If therefore thou shalt not watch, I will come on thee as a thief, and thou shalt not know what hour I will come upon thee. (Revelation 3:3)). It is applied to Judas (John 12:66This he said, not that he cared for the poor; but because he was a thief, and had the bag, and bare what was put therein. (John 12:6)). The word “thief” in the AV is always this word except in the passages quoted under No. 1.