Unit  n. 1 a individual thing, person, or group, esp. For calculation. B smallest component of a complex whole. 2 quantity as a standard of measurement (unit of heat; si unit). 3 smallest share in a unit trust. 4 part of a mechanism with a specified function. 5 fitted item of furniture, esp. As part of a set. 6 subgroup with a special function. 7 group of buildings, wards, etc., in a hospital. 8  a single-digit number. B the number ‘one’. [latin unus one]