Strong's #5100: tis (pronounced tis)
 an enclitic indefinite pronoun; some or any person or object:--a (kind of), any (man, thing, thing at all), certain (thing), divers, he (every) man, one (X thing), ought, + partly, some (man, -body, - thing, -what), (+ that no-)thing, what(-soever), X wherewith, whom(-soever), whose(-soever).
Thayer's Greek Lexicon:
 ́ 
 
  tis 
 
 1) a certain, a certain one
 2) some, some time, a while
 
  Part of Speech: pronoun
Relation: an enclitic indefinite pronoun
 
Usage:
This word is used 460 times:
Acts 9:19: "Then was Saul  certain days with the disciples"
Acts 9:33: "And there he found  a certain man named Aeneas, which had kept his bed"
Acts 9:36: "there was at Joppa  a certain disciple named Tabitha, which"
Acts 9:43: "in Joppa with  one Simon a tanner."
Acts 10:1: "There was  a certain man in Caesarea called Cornelius,"
Acts 10:6: "He lodgeth with  one Simon a tanner, whose house"
Acts 10:11: "heaven opened, and  a certain vessel descending unto him,"
Acts 10:23: "went away with them, and  certain brethren from Joppa"
Acts 10:47: "Can  any man forbid water, that these should not be baptized,"
Acts 10:48: "prayed they him to tarry  certain days."
Acts 11:5: "a trance I saw a vision,  A certain vessel descend, as it had been a great"
Acts 11:20: "And  some of them were men of Cyprus and"
Acts 11:29: "disciples, every man according to  his ability, determined to send relief"
Acts 12:1: "stretched forth his hands to vex  certain of the church."
Acts 13:1: "that was at Antioch  certain prophets and teachers; as"
Acts 13:6: "unto Paphos, they found  a certain sorcerer, a false prophet, a Jew, whose"
Acts 13:41: "ye shall in no wise believe, though  a man declare it unto you."
Acts 14:8: "And there sat  a certain man at Lystra, impotent in his feet,"
Acts 15:1: "And  certain men which came down from Judea taught the brethren,"
Acts 15:2: "and Barnabas, and  certain other"
Acts 15:2: "and Barnabas, and  certain other"
Acts 15:5: "But there rose up  certain of the sect of the Pharisees"
Acts 15:24: "Forasmuch as we have heard, that  certain which went out from us have troubled"
Acts 15:36: "And  some days after Paul said unto Barnabas,"
Acts 16:1: "Lystra: and, behold,  a certain disciple was there, named"
Acts 16:1: "named Timothy, the son  of a certain woman, which was a Jewess, and believed; but"
Acts 16:12: "that city abiding  certain days."
Acts 16:14: "And  a certain woman named Lydia, a seller of purple, of the city of Thyatira,"
Acts 16:16: "went to prayer,  a certain damsel possessed with a spirit of divination"
Acts 17:4: "And  some of them believed, and consorted with Paul"
Acts 17:5: "moved with envy, took unto  them certain lewd fellows of the baser sort,"
Acts 17:6: "they drew Jason and  certain brethren unto the rulers of the city,"
Acts 17:18: "Then  certain philosophers of the Epicureans, and of the Stoics,"
Acts 17:18: "encountered him. And  some said, What will"
Acts 17:20: "For thou bringest  certain strange things to our ears: we would"
Acts 17:21: "either to tell, or to hear  some new thing.)"
Acts 17:25: "men's hands, as though he needed  any thing, seeing he giveth to all life,"
Acts 17:28: "and have our being; as  certain also of your own poets"
Acts 17:34: "Howbeit  certain men cleaved unto him, and believed: among"
Acts 18:2: "And found  a certain Jew named Aquila, born in Pontus,"
Acts 18:7: "thence, and entered into  a certain man's house, named Justus, one that worshipped"
Acts 18:14: "If it were  a matter of wrong or wicked"
Acts 18:23: "And after he had spent  some time there, he departed, and went over all the country"
Acts 18:24: "And  a certain Jew named Apollos, born at Alexandria, an eloquent"
Acts 19:1: "Ephesus: and finding  certain disciples,"
Acts 19:9: "But when  divers were hardened, and believed not, but spake evil of that way"
Acts 19:9: "daily in the school  of one Tyrannus."
Acts 19:13: "Then  certain of the vagabond Jews, exorcists, took upon"
Acts 19:24: "For  a certain man named Demetrius, a silversmith, which made silver shrines"
Acts 19:31: "And  certain of the chief of Asia, which were his friends,"