The definition of wean is to withdraw by small degrees, or to get a small child or animal off of its mother's milk and onto other food.(verb)
An example of wean is when you stop breastfeeding and start feeding your child food.
See wean in Webster's New World College Dictionary
Origin: ME wenen < OE wenian, to accustom, train, with sense of awenian, to wean < a- (< af-, away) + wenian < IE base *wen-, to desire, attain, be satisfied > L venus, love
Origin: contr. of Scot wee ane, little one
See wean in American Heritage Dictionary 4
transitive verb weaned, wean·ing, weans
Origin: Middle English wenen
Origin: , from Old English wenian; see wen-1 in Indo-European roots. Usage Note: In recent years weaned on has come to be widely used in the sense “raised on,” as in Moviegoers weaned on the Star Trek TV series will doubtless find the film to their liking. A few critics have objected to this usage on the grounds that wean refers literally to a detachment from a source of nourishment. But the process of weaning involves a substitution of some other form of nourishment for mother's milk; thus it is sometimes said that a child is weaned onto or on sugar water. Hence a sentence like Paul was weaned on folk music may suggest metaphorically that Paul's exposure to folk music began from the time he stopped nursing, that is, from a very early age.
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