Seeing those frilly petals makes me smile—'carnation' in Hindi is most commonly called गुलबहार, pronounced roughly as 'gulbahaar' or 'gulbahar' (गुलबहार). If you're speaking casually, many people also just use the loanword कर्नेशन or कार्नेशन, written in Devanagari as 'कर्नेशन' or 'कार्नेशन', especially in markets or flower shops where English names stick. Botanically the plant is Dianthus caryophyllus, but everyday conversation will usually use गुलबहार or the transliterated form.
I grew up around neighborhood flower sellers, and I noticed different regions and speakers have their preferences: older folks might say गुलबहार, while younger vendors lean toward 'carnation' in Hindi script. Carnations are popular for garlands, bouquets, and festivals, and their many colors carry meanings—pink for gratitude, red for love, white for purity—so the Hindi name gets used a lot during celebrations. Personally, I love how the name गुलबहार feels poetic and warm, matching the soft texture of the blossoms.