Suppletion is when a word's different forms have different etymologies, leading to inflections ranging from translucent to completely opaque. For example, in English, good and better have different roots, as do bad and worse. It's really interesting to track the strange ways different forms of words gain popularity or fall out of use. To be in English is a really funky case because it comes from three different Old English verbs: beon, "be, become," eom, "remain," and wesan, also roughly "remain." As late as the 1500s, we used these verbs separately in certain forms: "I be," "thou beest," "they beth," before our tenses crystallized into the totally standardized but deeply weird set of be, being, been, am, are, is, was, and were.
In a looser sense, suppletion can refer to words that are related in meaning but not in origin. Obviously we have a boatload of these in English because of the different languages we've borrowed from. In the case of collateral adjectives, the adjective normally used with a given noun is etymologically unrelated: moon and lunar, horse and equine, brother and fraternal. These examples are all nouns derived from Proto-Germanic and adjectives from Latin, which is very common.
Your trivia question today is about (loose) suppletion. Name two collateral adjectives in English that correspond to two mysterious nouns: they appeared in Old English inexplicably, with no plausible root in Proto-Germanic, Latin, or any other language linguistic historians have explored.