late 14c., basken "to wallow (in blood)," from O.N. baðask, reflexive of baða "bathe" (see bathe). Modern meaning "soak up a flood of warmth" is apparently due to Shakespeare's use of the word in reference to sunshine in "As You Like It" (1600).
1742, prp. adj. from bask (q.v.). Basking shark is recorded from 1769.