Did you know onion belongs to the Lily family botanically speaking? Its scientific name is Allium Cepa.
Onion is used to give bulk in gravies in many dishes. It gives an excellent taste but onion has a limitation. The foods in which it is used get spoilt quickly owing to creation of moisture.
Onions once cut or made into a paste start spoiling quickly, so must be used immediately. Some people 'immerse' it in turmeric powder but may not be a foolproof solution.
Even with this it is difficult to preserve it for long.
Onion has medicinal uses too! It is used in eye drops for curing cataract.