weakling n.

c. 1300, from Old Norse veikr "weak," cognate with Old English wac "weak, pliant, soft," from Proto-Germanic *waika- "yield" (source also of Old Saxon wek, Swedish vek, Middle Dutch weec, Dutch week "weak, soft, tender," Old High German weih "yielding, soft," German weich "soft"), from PIE root *weik- (2) "to bend, to wind."

Sense of "lacking authority" is first recorded early 15c.; that of "lacking moral strength" late 14c. In grammar, denoting a verb inflected by regular syllabic addition rather than by change of the radical vowel, from 1833. Related: Weakly. Weak-kneed "wanting in resolve" is by 1856; older in a literal sense.

diminutive word-forming element, early 14c., from Old English -ling a nominal suffix (not originally diminutive), from Proto-Germanic *-linga-; attested in historical Germanic languages as a simple suffix, but probably representing a fusion of two suffixes: 1. that represented by English -el (1), as in thimble, handle; and 2. -ing, suffix indicating "person or thing of a specific kind or origin;" in masculine nouns also "son of" (as in farthing, atheling, Old English horing "adulterer, fornicator"), from PIE *-(i)ko- (see -ic).

Both these suffixes had occasional diminutive force, but this was only slightly evident in Old English -ling and its equivalents in Germanic languages except Norse, where it commonly was used as a diminutive suffix, especially in words designating the young of animals (such as gæslingr "gosling"). Thus it is possible that the diminutive use that developed in Middle English is from Old Norse.