One of the impoant defence mechanism is
Repression is a primary defence mechanism and is defined as unconsciously excluding from conscious awareness of anxiety-provoking ideas and /or feelings. eg in normal life: forgetting and slips of the tongue (Ref: a sho textbook of psychiatry, Niraj Ahuja,7th edition, pg no 207)
Alienation
Confabulation
Repression
Suppression
Cognitive development and defence mechanism