1. An idealized concept of a loved one, formed in childhood and retained unaltered in adult life.
2. Entomology. An adult insect.
She pictured him retaining, year after year, her imago in his heart, as strongly as his was impressed upon her own at that moment.
-- Ellen Wallace, King's Cope: a novel
Imago is a term that originated in psychoanalysis but migrated into popular usage in the 20th Century.