Answer:
Forensic.
Step-by-step explanation:
The use of the prefix -fore is a means of making a new word to the already existing and independent word. The new word is different from the parent word, which enables/makes it an independent word of its own too. therefore, forearm and foreshadowing are such types of words, which are made from the parent word "arm" and "shadowing" with the addition of the prefix -fore.
Unlike the two, the word "forensic" is a word of its own, without the use of a prefix.