the.com/soaker

means A big, heavy splash or dunking — a drenching soak delivered all at once, often with gleeful intent.

from Straightforward agent-noun formation: 'soak' (to drench thoroughly in liquid, traced back to Old English 'socian', related to 'suck') plus the '-er' suffix marking the thing or act that does the soaking. No hidden backstory here — it's the plain mechanics of English word-building, though the word's slangy, gleeful edge (the oversized splash, the cannonball, the surprise bucket of water) comes from informal usage layering drama onto a very ordinary verb.