late 14c., blober "a bubble, bubbling water; foaming waves," probably echoic of bubbling water. Original notion of "bubbling, foaming" survives in the figurative verbal meaning "to weep, cry" (c. 1400). Meaning "whale fat" first attested 1660s; earlier it was used in reference to jellyfish (c. 1600) and of whale oil (mid-15c.). Compare bubble.
"to cry, to overflow with weeping" (usually disparaging), c. 1400, from blubber (n.). In Middle English also "to seethe, bubble" (late 14c.). Related: Blubbered; blubbering.