confirm, be courageous (of good courage, stedfastly minded, strong, stronger), establish, fortify, harden, increase, prevail, strengthen (self), make strong (obstinate, speed)

Concise Bible Dictionary:

Paul and Barnabas went to Lystra, Iconium, and Antioch, confirming the souls of the disciples, and exhorting them to continue in the faith. Judas and Silas, messengers from Jerusalem to Antioch, being prophets, exhorted the brethren with many words and confirmed them. Again Paul and Silas went through Syria and Cilicia, confirming the churches (Acts 14:22; Acts 15:32,41). These passages, with Acts 18:23, where the word is translated “strengthen,” are all the places where the word ἐπιστηρίζω occurs. (There is no idea of any ceremonial, like what is now called “Confirmation.”)

Strong’s Dictionary of Hebrew Words:

Transliteration:
’amats
Phonic:
aw-mats’
Meaning:
a primitive root; to be alert, physically (on foot) or mentally (in courage)
KJV Usage:
confirm, be courageous (of good courage, stedfastly minded, strong, stronger), establish, fortify, harden, increase, prevail, strengthen (self), make strong (obstinate, speed)