What's the adjective for parentheses? Here's the word you're looking for.
Included below are past participle and present participle forms for the
verbs parenthesize and parenthesise which may be used as adjectives within certain contexts.
parenthetical
using, containing, or within parentheses (like this)
“Providing parenthetical information or explanatory footnotes on those not discussed in the introductions might have been more helpful than relegating the information to the index.”
