adj

• (masonry) Of a brick: unburnt.
• (zoology)
  "[…] Calais and Zetes had no beard upon their chin, / They both were callow. But aſſone as haire did once begin / In likeneſſe of a yellow Downe upon their cheekes to ſprout, / Then (euen as comes to paſſe in Birdes) the feathers budded out / Togither on their pinyons too, and ſpreaded round about / On both their ſides."
• (zoology)
  "Those three young men are particularly callow youths."
• (zoology)
  "a callow bee"

noun

• (entomology) Synonym of teneral (“an insect or other arthropod such as a spider which has just undergone ecdysis (“shedding of the exoskeleton”) and so lacks colour or firmness”).
• (geology) An alluvial flat.
• (UK, regional, mining, archaic) The upper layer of rubble in a quarry which has to be removed to reach the material to be mined.
• (obsolete)

adj

• (Ireland) Of land: low-lying and near a river, and thus regularly submerged.
  "The Bogs that extend along the western part of this District do not lie close to the Shannon, as those on the east side do along the banks of the Inny; they are separated from the river by a long tract of high, dry, callow land, subject, immediately near the river, to being overflowed in winter, but affording meadow, pasture, and in some places good arable land."

noun

• (Ireland) A low-lying meadow near a river which is regularly submerged.
  "Near-synonyms: bog, fen, marsh, swamp, mire, moor, slough"