1.The act or practice of deceiving; deception.
2. A stratagem; a trick.
3. The quality of being deceitful; falseness.
It has origins in Middle English deceite as well from from Old French, from past participle of deceveir, to deceive;
Everyday we use deceipt, whether it is being false to other people in the form of friendships, care and concern about their personal issues; or to work in that we take personal time instead of doing work for the employer. Most of all, we use it on ourselves, deceiving ourselves of the truth of a situation, pretending to be happy when in fact we may be the complete opposite.It isn't right, but it is a hard habit to break but it is worth being honest if only with ourselves though honesty is also something that should and could be toned down in the right circumstances but that is another day.
But it also has another use,
Deceit of lapwing: a flock of lapwing—Lipton, 1970.
As you may know, I love the use of language and particularly of words used to group things together. Being of an age group that learnt collective nouns for groups of animals and crows. This was a new term for Lapwings, and I was fascinated by the name similarly a murder of crows.. how it came about, I have no idea but I think it is great.