I'm looking for a seven letter word.
(P's)(I's)(S's)
wispsuauntrimmtuerngermn
The 7-letter answer is:
SEASONS - since, as per the title, the names of the four seasons are hidden here.
As if we...
...break down each of the English 6-letter names of the four seasons (i.e. specifically using 'Autumn' instead of 'Fall') into 2-letter chunks and consider the first 2 letters as their 'prefixes' (P's), the middle 2 letters as their 'infixes' (I's), and the last 2 letters as their 'suffixes' (S's), then these 'chunks' can be seen to make up the long string of letters when ordered in such a way that (i) all their prefixes are concatenated together, then (ii) all infixes, then (iii) all suffixes, as per the mysterious instruction in bold in the puzzle.
This should be easier to see if we break it up with some punctuation marks:
wispsuauntrimmtuerngermn
wi-sp-su-au / nt-ri-mm-tu / er-ng-er-mn
So the first prefix, infix and suffix together make 'winter', the next 'spring', then 'summer' and 'autumn' - which is also the order of the four seasons in a calendar year.