सादृश्याद्वा शृङ्गं दंष्ट्रेत्युच्यते, 'चत्वारि शृङ्गा' इति श्रुतेः ।चत्वारो भुजा अस्येति चतुर्भुजः ॥
In plain words
Or else 'horn' here means 'tusk', since the two look alike — the Veda itself says 'four horns'. He has four arms: hence Caturbhuja, the four-armed.
Close to the Sanskrit
Or, on account of resemblance, the horn is called a tusk, since the Veda says 'four horns'. His arms are four — thus, Caturbhuja, the four-armed.