The term SEEN-IT-ALL can be summarized as someone who is blase, which is a 5 letter word. Blase is an adjective used to describe someone who is indifferent or unimpressed due to having experienced too much of something. This could be due to having seen too much of the same thing, or having been exposed to too many different experiences. Someone who is blase is often jaded and bored, and may not be easily impressed.