late 14c., megre (late 12c. as a surname), "lean, thin, emaciated" (of persons or animals), from Old French megre, maigre "thin" (12c.), from Latin macrum (nominative macer) "lean, thin" (source of Spanish, Portuguese, and Italian magro), from PIE root *mak- "long, thin." Compare emaciate.
Of material things (land, food, etc.) from early 15c. Cognate Germanic words (Old Norse magr "thin," Old High German magar, German mager, Middle Dutch magher, Dutch mager, Old English mæger) come directly from the PIE root via Proto-Germanic *magras and are not from Latin.
word-forming element denoting action, quality, or state, attached to an adjective or past participle to form an abstract noun, from Old English -nes(s), from Proto-Germanic *in-assu- (cognates: Old Saxon -nissi, Middle Dutch -nisse, Dutch -nis, Old High German -nissa, German -nis, Gothic -inassus), from *-in-, originally belonging to the noun stem, + *-assu-, abstract noun suffix, probably from the same root as Latin -tudo (see -tude).
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Definitions of meagerness from WordNet
the quality of being meager; "an exiguity of cloth that would only allow of miniature capes"-George Eliot;