Vine's Expository Dictionary of NT Words 
"august, reverent," the masculine gender of an adjective (from sebas, "reverential awe"), became used as the title of the Roman emperor, Acts 25:21,25 , RV, for AV, "Augustus;" then, taking its name from the emperor, it became a title of honor applied to certain legions or cohorts or battalions, marked for their valor, Acts 27:1 . Cp. sebazomai, "to worship," Romans 1:25; sebasma, "an object of worship," Acts 17:23; 2—Thessalonians 2:4 .
King James Dictionary 
EM'PEROR, n. L. imperator, from impero, to command.
Literally, the commander of an army. In modern times, the sovereign or supreme monarch of an empire a title of dignity superior to that of king as the emperor of Germany or of Russia.
Webster's Dictionary 
(n.) The sovereign or supreme monarch of an empire; - a title of dignity superior to that of king; as, the emperor of Germany or of Austria; the emperor or Czar of Russia.
Hastings' Dictionary of the New Testament 
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
(Lat. imperator, general), a title common (in its Latin form) to all governors who had paramount jurisdiction within a given province (Smith, Diet. of Class. Antiq. s.v. Imperium), but technically assumed as a praenomen first by Julius Caesar (Sueton. Jul. 76), as affecting supreme power, and historically attributed to his successors, the heads of the so- styled Roman Empire (See Roman Empire) (q.v.). They were also designated as CAESAR (See Caesar) (q.v.). We are here chiefly concerned with them as they came in contact with the Christian religion in the character of persecutors or patrons. (See Persecution). (See Baldwin, Edicta vett. principum Roman. de Christianis, Hal. 1727 [also in Heineccii Jurispr. Romans 1:1374 sq.]; Crause, De Romanorum Imperatoribus Haereticis, viz. 1674; Hebenstreit, De Primis Christianis Imperatoribus, Jen. 1702; Heineccius, De Ministris Caesarun Christianis, Hal. 1712; also Hirt, De Imperatorun Ante Constant. Erga Christianos Favore, Jen. 1758; Koepke, De Statu Christianorum Sub Impp. Berol. 1828).
The following is a complete list of the Roman emperors, with their respective dates of accession.
Year of the 4 Emperors
(ends with Vespasian)
5 Good Emperors
(The next cluster of emperors is not part of a specific dynasty or other common grouping, but includes 4 from the year of the 5 emperors, 193.)
(More emperors without a dynastic label, although it includes the year of the 6 emperors, 238.) For more on this age of chaos, read Brian Campbell's excellent synopsis in The Romans and Their World.
235 - 238 Maximinus 238 Gordian I and II 238 Balbinus and Pupienus 238 - 244 Gordian III 244 - 249 Philip the Arab 249 - 251 Decius 251 - 253 Gallus 253 - 260 Valerian 254 - 268 Gallienus 268 - 270 Claudius Gothicus 270 - 275 Aurelian 275 - 276 Tacitus 276 - 282 Probus 282 - 285 Carus Carinus Numerian
286?-297? British Emperors 286/7-293 Carausius 293-296/7 Allectus
293-306 Constantius I Chlorus
Dynasty of Constantine
293-311 Galerius 305-313 Maximinus Daia 305-307 Severus II 306-312 Maxentius 308-309 L. Domitius Alexander 308-324 Licinius 314? Valens 324 Martinianus 306-337 Constantinus I 333/334 Calocaerus 337-340 Constantinus II 337-350 Constans I 337-361 Constantius II 350-353 Magnentius 350 Nepotian 350 Vetranio 355 Silvanus 361-363 Julianus 363-364 Jovianus
(More emperors without a dynastic label)
364-375 Valentinianus I 375 Firmus 364-378 Valens 365-366 Procopius 366 Marcellus 367-383 Gratian 375-392 Valentinianus II 378-395 Theodosius I 383-388 Magnus Maximus 384-388 Flavius Victor 392-394 Eugenius
395-423 Honorius[Division of the Empire - Honorius' brother Arcadius ruled the East 395-408] 407-411 Constantine III usurper 421 Constantius III 423-425 Johannes 425-455 Valentinian III 455 Petronius Maximus 455-456 Avitus 457-461 Majorian 461-465 Libius Severus 467-472 Anthemius 468 Arvandus 470 Romanus 472 Olybrius 473-474 Glycerius 474-475 Julius Nepos 475-476 Romulus Augustulus
International Standard Bible Encyclopedia 
emp´ẽr - ẽr ( ὁ σεβαστός , ho sebastós ; Latin augustus : The title of the Roman emperors; Acts 25:21 , Acts 25:25 ). See Augustus; Caesar .
- Emperor from Vine's Expository Dictionary of NT Words
- Emperor from King James Dictionary
- Emperor from Webster's Dictionary
- Emperor from Hastings' Dictionary of the New Testament
- Emperor from Cyclopedia of Biblical, Theological and Ecclesiastical Literature
- Emperor from International Standard Bible Encyclopedia