Superman portrayer Christopher, in so many words

RAREEVENT

Think of how you might describe something that happens very infrequently, then consider the actor who famously played the Man of Steel in the 1970s.

This clue plays on the phrase "in so many words," hinting at a synonym for "rare" (meaning infrequent) rather than the actor's name. Christopher Reeve famously played Superman, but "Reeve" sounds like "reeve," which is homophonically clued as "rare event" when you think of "rare" + "event." The answer cleverly sidesteps the literal actor reference by turning his last name into a punny phrase.