A.T. Robertson Commentary Acts 11:28

"And there stood up one of them named Agabus, and signified by the Spirit that there should be a great famine over all the world: which came to pass in the days of Claudius." — Acts 11:28 (ASV)

Signified (εσημαινεν). Imperfect active in Westcott and Hort, but aorist active εσημανεν in the margin. The verb is an old one from σημα (σημειον) a sign (cf. the symbolic sign in 21:11). Here Agabus does predict a famine through the Holy Spirit.

Should be (μελλειν εσεσθα). Μελλω occurs either with the present infinitive (16:27), the aorist infinitive (12:6), or the future as here and 24:15; 27:10.

Over all the world (εφ' ολην την οικουμενην). Over all the inhabited earth (γην, understood). Probably a common hyperbole for the Roman empire as in Lu 2:1. Josephus (Ant. VIII. 13, 4) appears to restrict it to Palestine.

In the days of Claudius (επ Κλαυδιου). He was Roman Emperor A.D. 41-44. The Roman writers (Suetonius, Dio Cassius, Tacitus) all tell of dearths (assiduae sterilitates) during the brief reign of Claudius who was preceded by Caligula and followed by Nero.