Plural of flounder; flatfish with both eyes on one side, or third-person singular present tense of the verb 'to flounder'.
From Middle Dutch 'vlondre' (flatfish). The '-s' ending serves as both plural marker for the noun and third-person singular present tense marker for the verb.
A flounder is literally a fish that flops around awkwardly on land, so when humans 'flounder,' we're essentially acting like a fish out of water—which is exactly what 'out of your element' means!
Complete word intelligence in one call. Free tier — 50 lookups/day.