Wise, shrewd, perceptive; showing sound judgment and keen insight, especially in practical matters.
→ Synonyms of sagacious include insightful, discerning, astute (word 3 of Level 4), judicious (word 16 of Level 5), percipient (pur-SIP-eeint), sage (rhymes with page), sapient (SAY-pee-int), and perspicacious (PUR-spi-KAY-shus).
Antonyms of sagacious include undiscriminating, undiscerning, simpleminded, witless, inane (i-NAYN), gullible, credulous (KREJ-uhlus), obtuse (uhb-T(Y)OOS), and addlepated (AD-’l-PAY-tid).
The corresponding noun is sagacity, wisdom, shrewdness, keen insight or discernment.
Sagacious comes from the Latin sagax, having keen senses, especially a keen sense of smell. In its early days in the language, sagacious was used of hunting dogs to mean quick in picking up a scent. That sense is long obsolete. By 1755, when Samuel Johnson published his famous dictionary, sagacious had come to mean, as Johnson puts it, “quick of thought; acute in making discoveries.” To illustrate the expanded sense, Johnson quotes the philosopher John Locke: “Only sagacious heads light on these observations, and reduce them into general propositions.” Over the years since then, sagacious continued to acquire dignity, perhaps by association with the adjective sage, which means having or showing great wisdom. Today, says the third edition of The American Heritage Dictionary (1992), sagacious “connotes prudence, circumspection, discernment, and farsightedness.”
That’s a far cry from the hunting hounds of yore. Yet, as those words reveal, a faint odor of quick-sniffing canine instinct still clings to the word. In current usage, the sagacious person is no brooding scholar or musing philosopher but a shrewd, sharp-eyed, keen-witted person who displays instinctive wisdom, swift insight, and sound judgment regarding mundane or practical matters. Thus we do not speak of a sagacious treatise on the meaning of life, but rather of a sagacious comment on human nature, a shrewd lawyer who asks sagacious questions, or a business executive known for making sagacious decisions—in other words, wise and keenly perceptive decisions.
