Early Noldorin
-garn
suffix. *-made
-carn
suffix. *-made
carbh
noun. deed
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A suffixal form ᴱN. -carn or -garn of the passive participle agarn for the verb ᴱN. cara- “to make, do” in the Early Noldorin Dictionary of the 1920s, hence meaning something like “-✱made”.
Neo-Sindarin: I think this suffix can be salvaged as a reduction of the later passive participle carnen of S. car- “do, make”, which can be used to form adjectives such as adangarn “man-made”. It does conflict with S. carn “deed”, but I prefer S. carth for this noun form.