a colourless odourless relatively unreactive gaseous element that forms 78 per cent (by volume) of the air, occurs in many compounds, and is an essential constituent of proteins and nucleic acids: used in the manufacture of ammonia and other chemicals and as a refrigerant. Symbol: N; atomic no: 7; atomic wt: 14.00674; valency: 3 or 5; density:1⁄2506 kg/m3; melting pt: –210.00°C; boiling pt: –195.8°C

(as modifier)