late 14c., from O.Fr. considerer, from L. considerare "to look at closely, observe," lit. "to observe the stars," from com- "with" + sidus (gen. sideris) "constellation." Perhaps a metaphor from navigation, but more likely reflecting Roman obsession with divination by astrology. Tucker doubts the connection with sidus, however, since it is "quite inapplicable to desiderare," and suggests derivation instead from the root of Eng. side meaning "stretch, extend," and a sense for the full word of "survey on all sides" or "dwell long upon."