means A flat floating platform of logs, planks, or inflated material used to travel on or across water; also, informally, a large quantity of something.

from From Middle English 'raft' or 'rafte,' borrowed from Old Norse 'raptr' meaning a log, rafter, or beam — the same timber instinct that gave us the 'rafter' in a roof. The Norse were sailors and woodworkers, and the word carried their sense of stout structural wood from house-beam to water-borne platform. The colloquial 'a raft of things' (a whole pile) is a separate, later twist, possibly muddled with an unrelated dialect word for a heap.