The Quran

۞ وَما كانَ لِبَشَرٍ أَن يُكَلِّمَهُ اللَّهُ إِلّا وَحيًا أَو مِن وَراءِ حِجابٍ أَو يُرسِلَ رَسولًا فَيوحِيَ بِإِذنِهِ ما يَشاءُ ۚ إِنَّهُ عَلِيٌّ حَكيمٌ

Muhammad Asad

And it is not given to mortal man that God should speak unto him otherwise than through sudden¹ inspiration, or [by a voice, as it were,] from behind a veil, or by sending an apostle to reveal, by His leave, whatever He wills [to reveal]:² for, verily, He is exalted, wise.

This is the primary meaning of wahy, a term which combines the concepts of suddenness and inner illumination (Raghib); in the usage of the Qur'an, it is often, though by no means always, synonymous with "revelation". - The above passage connects with the first paragraph of verse 48, which speaks of the divine message entrusted to the Prophet.
Cf. 53:10.