Deep or deap?

• profound.
• vast.
• bottomless.
• abysmal.
• infinite.
• unfathomable.
• endless.
• boundless.

From Middle English depe, deep, dep, deop, from Old English dēop (“deep, profound; awful, mysterious; heinous; serious, solemn, earnest; extreme, great”), from Proto-West Germanic *deup, from Proto-Germanic *deupaz (“deep”), from Proto-Indo-European *dʰewbʰ-nós, from *dʰewbʰ- (“deep”).

deep (comparative deeper, superlative deepest)

deep (comparative more deep or deeper, superlative most deep or deepest)

deep (countable and uncountable, plural deeps)

Ultimately from Proto-West Germanic *deup. One of several Ripuarian relict words with an unshifted post-vocalic plosive. Compare Aap (“ape”), söke (“to seek”).

deep (masculine deepe, feminine deep or deepe, comparativer deeper, superlative et deepste)

deep

deep

From Middle Low German diep, from Old Saxon diop.

Things can even be figuratively deep when they are extreme, like "deep thoughts" or a "deep recession." The Old English word deop means "deep," but it also means, "awful, mysterious, and solemn."