The following prepositions are only used in compounds. Note: this is true in English as well as Latin. In the case of the prepositions in and post, only the forms that mean "not" and "forth, near" are restricted in this way. The forms that mean "in" and "after" are not subject to this restriction.

Latin Preposition, meaning.	Latin compound word, meaning.	English example using the preposition
ambi, around.	ambitio, going around.	ambient
dis, apart/not.	difficilis, not easy.	disability
in, not.	inimicus, unfriendly.	insufficient
pos(post), forth, near.	possidere, to sit near, to possess.	possess
re(red), back.	reclinis, leaning back.	retrieve
se(sed), apart.	secedere, to go apart.	select

Source: The Latin in English, by Harry Pratt Judson. 1897.