The phrase "past recall" refers to something that cannot be remembered or brought back into memory. Synonyms for this phrase include "beyond retrieval," "forgotten," "unrecoverable," "unforgettable," "lost to memory," and "unable to recollect." Other related phrases that can be used in the context of forgetting something are "slipped away," "faded into oblivion," "vanished," "disappeared," "wiped out," and "erased from memory." These synonyms and related phrases can be used in different contexts, such as personal experiences, historical events, and scientific phenomena. Overall, each of these words represents the inability to recollect something from the past.