soak (v.)

Middle English souken, from Old English sucan "draw liquid into the mouth by action of the tongue and lips," especially "draw milk from the breast or udder," from Proto-Germanic *suk- (source also of Old Saxon sugan, Old High German sugan, Old Norse suga, Danish suge, Swedish suga, Middle Dutch sughen, Dutch zuigen, German saugen "to suck"), from PIE root seue- "to take liquid," perhaps imitative, the source also of Latin sugere "to suck," succus "juice, sap;" Old Irish sugim, Welsh sugno "to suck." Compare sup (v.2). Related: Sucked; sucking. 

In reference to blood by mid-14c., of biting flies, etc. To suck the blood of figuratively as "to exhaust" is by 1580s. The disdainful slang expression suck eggs is attested by 1906; a suck-egg (c. 1600) was "a young fellow," also "silly person," but also an avaricious one, the last from the image of animals (especially the weasel) reputed to suck eggs. Sucks (n.) as an expression of contempt (sucks to you) is by 1913.

The meaning "do fellatio" is recorded by 1928. The slang sense of "be contemptible" is attested by 1971 (the underlying notion is felt as fellatio).

To suck hind tit "be inferior" is American English slang recorded by 1940.

The old, old saying that the runt pig always sucks the hind teat is not so far wrong, as it quite approximates the condition that exists. [The Chester White Journal, April 1921] 

"to sip, to take into the mouth with the lips, drink or swallow with small mouthfuls," Middle English soupen, from Old English supan (West Saxon), suppan, supian (Northumbrian) "sip, taste, drink, swallow" (strong verb, past tense seap, past participle sopen).

This is from Proto-Germanic *supanan (source also of Old Norse supa "to sip, drink," Middle Low German supen, Dutch zuipen "to drink, tipple," Old High German sufan, German saufen "to drink, booze"). The Germanic word is from PIE *sub-, possibly [Watkins] an extended form of the root *seue- (2) "to take liquid" (source also of Sanskrit sunoti "presses out juice," soma; Avestan haoma, Persian hom "juice;" Greek huetos "rain," huein "to rain;" Latin sugere "to suck," succus "juice, sap;" Lithuanian sula "flowing sap;" Old Church Slavonic soku "sap," susati "suck;" Middle Irish suth "sap;" Old English seaw "sap").

If this is correct, the two verbs sup are cognates out of Germanic, the other one via French. The noun meaning "a small quantity of liquid" is by 1560s.

"soft or marshy place, bog, quagmire," 1530s, a word of unknown origin. It is attested earlier as a verb, "to become soaked; to soak" (mid-15c.), and is perhaps related to soak (v.) or from or related to similar words in Scandinavian. Related: Sogged.