sidereal adj.

late 14c., "to fix the mind upon for careful examination, meditate upon," also "view attentively, scrutinize; not to be negligent of," from Old French considerer (13c.) "reflect on, consider, study," from Latin considerare "to look at closely, observe," probably literally "to observe the stars," from assimilated form of com "with, together" (see con-) + sidus (genitive sideris) "heavenly body, star, constellation" (see sidereal).

Perhaps a metaphor from navigation, but more likely reflecting Roman obsession with divination by astrology. Tucker doubts the connection with sidus, however, because it is "quite inapplicable to desiderare," and suggests derivation instead from the PIE root of English side meaning "stretch, extend," and a sense for the full word of "survey on all sides" or "dwell long upon."

From 1530s as "to regard in a particular light." Related: Considered; considering.

mid-15c., "capable of being considered, conceivable," from Medieval Latin considerabilis "worthy to be considered," from Latin considerare "to look at closely, observe," probably literally "to observe the stars," from assimilated form of com "with, together" (see con-) + sidus (genitive sideris) "heavenly body, star, constellation" (see sidereal).

Meaning "pretty large" is from 1650s (implied in considerably), from now-archaic earlier sense of "Worthy of regard or attention" (1610s).

CONSIDERABLE. This word is still frequently used in the manner pointed out by Dr. Witherspoon in the following remark: "He is considerable of a surveyor; considerable of it may be found in the country. This manner of speaking prevails in the northern parts." [Pickering, "A Vocabulary, or Collection of Words and Phrases Which Have Been Supposed to be Peculiar to the United States of America," 1816]

"sudden paralysis," especially of a part of the body, 1610s, from Latin siderationem (nominative sideratio) "blast, blight, palsy," from siderari "to be planet-struck, afflicted as if by an evil star," from stem of sidus (genitive sideris) "heavenly body, star, constellation" (see sidereal). English in 17c. also had siderated "blasted," literal or figurative.