-proof, used as the suffix to a noun, basically means that the object you are describing is resistant to the noun.
The specific example that led me to look for this was emailing our support team about a process we do that is not robust and highly prone to human error. I wanted the opposite of "idiot-proof", but couldn't think of it.
Error-prone. Idiot-prone.
Etymonline says regarding -prone:
c. 1400, "naturally inclined to something, apt, liable," from Latin pronus "bent forward, leaning forward, bent over," figuratively "inclined to, disposed," perhaps from adverbial form of pro-"before, for, instead of" (see pro-) + ending as in infernus, externus. Meaning "lying face-down" is first recorded 1570s. Literal and figurative senses both were in Latin; figurative is older in English. Related:Proneness.
