mis ‧ ap ‧ pre ‧ hen ‧ sion /ˌmɪsæprɪˈhenʃ ə n/ BrE AmE noun [countable]
formal a mistaken belief or a wrong understanding of something SYN misunderstanding
under a misapprehension
You seem to be under a misapprehension.
I think we should clear up this misapprehension.