तदा शैलाग्र शिखरे वामो हनुर् अभज्यत |
ततो हि नाम धेयम् ते हनुमान् इति कीर्तितम् || ४-६६-२४

when Indra hurled the thunderbolt at young anjineya (son of Anjana), he fell on the mountain top and broke his Zygomatic Arch (cheek bone) and hence got the name Hanumaan (one who has a broken cheek bone).

- Valmiki’s Ramayana