Meaning

noun a person who lacks confidence, is irresolute and wishy-washy

noun a hypothetical subatomic particle of large mass that interacts weakly with ordinary matter through gravitation; postulated as a constituent of the dark matter of the universe

originPossibly a clipping of whimper. The term was understood in the United States by the 1930s, as it was incorporated into the names of two famous media characters known for living up to that name: The devious but cowardly Popeye supporting-character called "J. Wellington Wimpy", and the soft-spoken character "Wallace Wimple" from the radio show Fibber McGee and Molly.

Etymology from Wiktionary, CC BY-SA 3.0