Synonyms of the word

unforgettable

• adj. Very difficult or impossible to forget.

haunting

• v. present participle of haunt.
• adj. Remaining in the mind; not easily forgotten.
• n. A particular instance of haunting; a ghostly habitation.

memorable

• adj. Worthy to be remembered; very important or remarkable.

persistent

• adj. Obstinately refusing to give up or let go.
• adj. Insistently repetitive.
• adj. Indefinitely continuous.
• adj. (botany) Lasting past maturity without falling off.
• adj. (computing) Of data or data structures: existing after the execution of the program. Remaining in existence…
• adj. (mathematics) Describing a fractal process that has a positive Brown function.
• adj. (mathematics, stochastic processes, of a state) non-transient.

red-letter

• adj. Particularly significant or positive.