The English word "angel" comes from the Greek angelos, which means 'messenger'. In the Old Testament, with two exceptions, the Hebrew word for "angel" is malak, also meaning 'messenger'. The prophet Malachi took his name from this word. He was himself a messenger, and he prophesied about the coming of "the messenger of the covenant", Jesus Christ (Malachi 3:1).
Although the word "angel" in the Bible, meaning a messenger, nearly always applies to heavenly beings, it can occasionally apply to human messengers. Malachi himself said a priest was a messenger (malak) of the LORD of hosts (Malachi 2:7), and in the Book of Revelation the elders of the seven churches of Asia were called angels (1:20; 2:1 etc.). But when we meet messengers doing supernatural things, there is no doubt they are heavenly beings - God's messengers, working for Him and for the ultimate benefit of mankind.