A common noun transformation rule in Sanskrit has -ഏശം, or -ഏഷം transforming to -ഇഷ്ടം. This changes the meaning of the noun to "that which has something" or "that which has been done something". Many common words in Malayalam follow this etymology.
Consider the famous title ചിന്താവിഷ്ടയായ സീത. The first word ചിന്താവിഷ്ട = ചിന്ത + ആവിഷ്ട means "consumed with thought". The second component ആവിഷ്ട comes from ആവേശം.
The current meaning of ആവേശം is enthusiam or energy. However, originally വേശം meant entry. So ആവേശം means to enter all over or to infuse. Thus, ആവിഷ്ട means one who has been possesed with the feeling making ചിന്താവിഷ്ട mean one who has been possed with thoughts or worries.
There are other similar examples:
ക്ലേശം (difficulty) -> ക്ളിഷ്ടം (that which is difficult)
ശേഷം (after) -> ശിഷ്ടം (remainder)
ആശ്ലേഷം (embrace) -> ആശ്ലിഷ്ടം (that which is embraced)
And there are some uncommon examples like
വേശം (entry) -> വിഷ്ടം (that which is entered, crossbeam)
ശ്ലേഷം (pun) -> ശ്ലിഷ്ടം (punny)
Can you think of other such examples?