Synonyms for Wimp (same or very similar meaning)
WordNet sense 1 (a person who lacks confidence, is irresolute and wishy-washy):
chicken, crybaby
WordNet sense 2 (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):
weakly interacting massive particle
From the ODE community, based on WordNet
add/edit