sip v.

late 14c., sippen, "drink little by little, drink in small mouthfuls" (sometimes glossing Latin potisso, subbibo), a word of uncertain origin, perhaps from a Continental Germanic word such as Low German sippen "to sip," or from Old English sypian "absorb, drink in," which is related to supan "to take into the mouth a little at a time" (see sup (v.2)). OED writes that it is, "possibly a modification of sup intended to express a slighter action."

Compare Middle English soupen "drink in small mouthfuls, from Old English supan. Also compare Dutch sipperlippen "taste with the tip of the tongue." The transitive sense of "drink (a liquid) in very small mouthfuls" is from c. 1600. Related: Sipped; sipper; sipping.

"a small drink; act of drinking by small quantities," by 1630s, perhaps c. 1500, from sip (v.). The figurative sense of "a mere taste" is by 1728.