1 oneness; being one, single, or individual; being formed of parts that constitute a whole; due interconnection and coherence of parts (disturbs the unity of the idea; the pictures lack unity; national unity).
2 harmony or concord between persons etc. (lived together in unity).
3 a thing forming a complex whole (a person regarded as a unity).
4 Math. the number 'one', the factor that leaves unchanged the quantity on which it operates.
5 Theatr. each of the three dramatic principles requiring limitation of the supposed time of a drama to that occupied in acting it or to a single day (unity of time), use of one scene throughout (unity of place), and concentration on the development of a single plot (unity of action).
Etymology: ME f. OF uniteacute f. L unitas -tatis f. unus one
Useful english dictionary. 2012.