word-forming element meaning variously "above; highest; across; higher in power or authority; too much; above normal; outer; beyond in time, too long," from Old English ofer (from PIE root *uper "over"). Over and its Germanic relations were widely used as prefixes, and sometimes could be used with negative force. This is rare in Modern English, but compare Gothic ufarmunnon "to forget," ufar-swaran "to swear falsely;" Old English ofercræft "fraud."
In some of its uses, moreover, over is a movable element, which can be prefixed at will to almost any verb or adjective of suitable sense, as freely as an adjective can be placed before a substantive or an adverb before an adjective. [OED]
Among the old words not now existing are Old English oferlufu (Middle English oferlufe), literally "over-love," hence "excessive or immoderate love." Over- in Middle English also could carry a sense of "too little, below normal," as in over-lyght "of too little weight" (c. 1400), overlitel "too small" (mid-14c.), overshort, etc.
1550s, "stage in growing," from grow + -th (2), on model of health, stealth, etc. Compare Old Norse groði, from groa "to grow." Meaning "that which has grown" is from 1570s; "process of growing" is from 1580s. Old English used grownes "increase, prosperity."
late 14c., "covered with growth," past-participle adjective from overgrow "to cover, overspread (with foliage);" late 14c., overgrouen, see over- + grown, and compare Old English verb ofergrowan. Meaning "having grown too large, grown beyond the fit or natural size" is attested from late 15c.
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Definitions of overgrowth from WordNet
excessive size; usually caused by excessive secretion of growth hormone from the pituitary gland;