"physician" (obsolete, poetical, or archaic), from Old English læce "leech," probably from Old Danish læke, from Proto-Germanic *lekjaz "enchanter, one who speaks magic words; healer, physician" (source also of Old Frisian letza, Old Saxon laki, Old Norse læknir, Old High German lahhi, Gothic lekeis "physician"), literally "one who counsels," perhaps connected with a root found in Celtic (compare Irish liaig "charmer, exorcist, physician") and Slavic (compare Serbo-Croatian lijekar, Polish lekarz), from PIE *lep-agi "conjurer," from root *leg- (1) "to collect, gather," with derivatives meaning "to speak (to 'pick out words')."

For sense development, compare Old Church Slavonic baliji "doctor," originally "conjurer," related to Serbo-Croatian bajati "enchant, conjure;" Old Church Slavonic vrači, Russian vrač "doctor," related to Serbo-Croatian vrač "sorcerer, fortune-teller." The form merged with leech (n.1) in Middle English, apparently by folk etymology. In early Middle English the word also was used of God and Christ; but by 17c. the sense had so deteriorated that leech typically was applied only to veterinary practitioners, and soon it was entirely archaic.

The fourth finger of the hand, in Old English, was læcfinger, translating Latin digitus medicus, Greek daktylus iatrikos, supposedly because a vein from that finger stretches straight to the heart.

familiar form of doctor, attested from 1850.

"relating or pertaining to the degree of a doctor or to one who holds such a degree," 1560s; see doctor (n.) + -al (1).

"the degree of a doctor," 1670s; see doctor (n.) + -ate (1).

late 14c., "the body of principles, dogmas, etc., in a religion or field of knowledge," from Old French doctrine (12c.) "teaching, doctrine" and directly from Latin doctrina "a teaching, body of teachings, learning," from doctor "teacher" (see doctor (n.)) + -ina, fem. of -inus, suffix forming fem. abstract nouns (see -ine (1)).

The notion is "whatever is taught or laid down as true by a master or instructor," hence "any set of principles held as true." In Middle English, it could be used generally for "learning, instruction, education." In U.S. history, the Monroe doctrine was put forward in a message to Congress Dec. 2, 1823; the exact phrase is attested by 1848.

Proto-Indo-European root meaning "to take, accept."

It forms all or part of: condign; dainty; decent; decor; decorate; decorous; deign; dignify; dignity; diplodocus; disciple; discipline; disdain; docent; Docetism; docile; docimacy; doctor; doctrine; document; dogma; dogmatic; doxology; heterodox; indignance; indignant; indignation; indignity; orthodox; paradox; synecdoche.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit daśasyati "shows honor, is gracious," dacati "makes offerings, bestows;" Greek dokein "to appear, seem, think," dekhesthai "to accept;" Latin decere "to be fitting or suitable," docere "to teach," decus "grace, ornament."