Which word that has 'ct' in and ends with 'um' is the most popular word?As far as popular words go, there's 'dictum' which is the 30136th most common word.
Which word in particular from this list has the largest character count?The biggest word on this list is 'propionibacterium'. It consists of 17 characters.
What is an unusual word on this list?The most unusual word in our opinion is 'spectrum'. The dictionary defines it as "1. An apparition; a specter. [Obs.] 2. (Opt.) (a) The several colored and other rays of which light is composed, separated by the refraction of a prism or other means, and observed or studied either as spread out on a screen, by direct vision, by photography, or otherwise. See Illust....".
How many words are there using this combination of letters?From this page of words that contain 'ct' and end in 'um', there are 97 effective combinations which are possible altogether.
What's the highest scoring word in Scrabble using the requested combination ?It is possible to make 'affectum' which scores 18 points.