Literally refers to the nose or nostrils — the organ of breathing and, by extension, the visible sign of anger (heavy, flaring breath). The dual form ʾappayim means 'nostrils' or 'face.' In its metaphorical sense, ʾaph is the most common Hebrew word for anger, particularly divine wrath. The connection between breathing and emotion is deeply embodied: anger is literally hot breath through the nostrils.
The phrase ʾerek ʾappayim — literally 'long of nostrils,' meaning slow to anger — is one of God's defining self-descriptions (Exod 34:6; Num 14:18; Ps 86:15). It first appears in the great theophany of Exodus 34, where God proclaims His own name and character after Israel's golden calf apostasy. That God is 'slow to anger' does not mean He lacks wrath — ʾaph describes His fierce response to sin throughout the prophets — but that His patience is vast, His mercy preceding judgment. The interplay between ʾaph (anger) and ʾerek ʾappayim (patience) maps the tension of a holy God who is both just and merciful.