c. 1400, perhaps a causative or frequentative form of Middle English suken "to suck" (see suck), but OED suggests instead a back-formation from suckling (though this word is attested only from mid-15c.). Related: Suckled; suckling.
Old English sucan "to suck," from a Proto-Germanic word of imitative origin (cognates: Old Saxon, Old High German sugan, Old Norse suga, Danish suge, Swedish suga, Middle Dutch sughen, Dutch zuigen, German saugen "to suck"), possibly from the same source as Latin sugere "to suck," succus "juice, sap;" Old Irish sugim, Welsh sugno "to suck;" see sup (v.2). As a noun from c. 1300.
Meaning "do fellatio" is first recorded 1928. Slang sense of "be contemptible" first attested 1971 (the underlying notion is of fellatio). Related: Sucked; sucking. Suck eggs is from 1906. Suck hind tit "be inferior" is American English slang first recorded 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]
mid-15c., "infant at the breast," from suck + diminutive suffix -ling. Similar formation in Middle Dutch sogeling, Dutch zuigeling, German Säugling. Meaning "calf or other young mammal" is from 1520s. Meaning "act of breast-feeding" is attested from 1799. Adjectival sense "not yet weaned" is from 1799.
<a href="https://www.etymonline.com/word/suckle">Etymology of suckle by etymonline</a>
Harper, D. (n.d.). Etymology of suckle. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/suckle