Etymology
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adviser (n.)
1610s, "one who gives advice," agent noun from advise (v.). Meaning "faculty assigned to mentor students" is from 1887. Meaning "military person sent to help a government or army in a foreign country" is recorded from 1915. Alternative form, Latinate advisor, is perhaps a back-formation from advisory.
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-er (1)

English agent noun ending, corresponding to Latin -or. In native words it represents Old English -ere (Old Northumbrian also -are) "man who has to do with," from Proto-Germanic *-ari (cognates: German -er, Swedish -are, Danish -ere), from Proto-Germanic *-arjoz. Some believe this root is identical with, and perhaps a borrowing of, Latin -arius (see -ary).

Generally used with native Germanic words. In words of Latin origin, verbs derived from past participle stems of Latin ones (including most verbs in -ate) usually take the Latin ending -or, as do Latin verbs that passed through French (such as governor); but there are many exceptions (eraser, laborer, promoter, deserter; sailor, bachelor), some of which were conformed from Latin to English in late Middle English.

The use of -or and -ee in legal language (such as lessor/lessee) to distinguish actors and recipients of action has given the -or ending a tinge of professionalism, and this makes it useful in doubling words that have a professional and a non-professional sense (such as advisor/adviser, conductor/conducter, incubator/incubater, elevator/elevater).

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mentor (n.)

"wise adviser, intimate friend who also is a sage counselor," especially of one who is young or inexperienced, 1750, from Greek Mentor, friend of Odysseus and adviser of Telemachus (but often actually Athene in disguise) in the "Odyssey." The name perhaps ultimately means "adviser," because in form it is an agent noun of mentos "intent, purpose, spirit, passion" from PIE *mon-eyo- (source also of Sanskrit man-tar- "one who thinks," Latin mon-i-tor "one who admonishes"), causative form of root *men- (1) "to think." Compare monitor (n.). Often capitalized, even in the general sense, into mid-19c. The general use of the word probably is via later popular romances, in which Mentor played a larger part than he does in Homer. Related: Mentorship.

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reader (n.)

Old English rædere "one who counsels; person who reads aloud to others; lector; scholar; diviner, interpreter," agent noun from rædan (see read (v.)) in its various senses. Compare Dutch rader "adviser," Old High German ratari "counselor." The Old English fem. form was rædistre. Meaning "a reading book for schools" is by 1789.

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counselor (n.)

mid-13c., counseiler, "one who gives counsel or advice, a confidante," from Old French conseillier "counselor, adviser" (Modern French conseiller), from Latin consilator, agent noun from consiliare, from consilium (see counsel (v.)).

Also sometimes counsellor, but the double -l- is unetymological and perhaps is modeled on chancellor. Meaning "one who gives professional legal advice, a counseling lawyer," is from 1530s. Psychological sense (as in marriage counselor, is from 1940).

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comforter (n.)

mid-14c., "one who consoles or supports in distress, anger, etc." (originally in religious use, with capital C-, "the Holy Ghost"), from Anglo-French confortour (Old French conforteor) "helper, adviser, supporter," from Vulgar Latin *confortatorem, agent noun from Late Latin confortare "to strengthen much" (see comfort (v.)). As a kind of knitted, crocheted scarf fit for tying around the neck in cold weather, from 1817; as a kind of quilted coverlet, from 1832.

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lawyer (n.)

late 14c. lauier, lawer, lawere (mid-14c. as a surname), "one versed in law, one whose profession is suits in court or client advice on legal rights," from Middle English lawe "law" (see law) + -iere. Spelling with -y- predominated from 17c. (see -yer). In the New Testament (Luke xiv.3, etc.) "interpreter of Mosaic law." Old English had lahwita, with wita "sage, wise man; adviser councilor," and an earlier Middle English word for "lawyer" was man-of-law (mid-14c.). Related: Lawyerly.

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assessor (n.)
late 14c., "assistant or adviser to a judge or magistrate," from Old French assessor "assistant judge, assessor (in court)" (12c., Modern French assesseur) and directly from Latin assessor "an assistant, aid; an assistant judge," in Late Latin "one who assesses taxes," literally "a sitter-by, one who sits by (another)," agent noun from past participle stem of assidere "to sit beside" (see assess). From 1610s as "one who assesses taxes." Milton uses it in the literal Latin sense in "Paradise Lost," calling Christ the Assessor of God's throne.
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mandarin (n.)

1580s, "Chinese official," via Portuguese mandarim or older Dutch mandorijn from Malay (Austronesian) mantri, from Hindi mantri "councilor, minister of state," from Sanskrit mantri, nominative of mantrin- "adviser," from mantra "counsel," from PIE root *men- (1) "to think." Form influenced in Portuguese by mandar "to command, order."

Used generically for the several grades of Chinese officials; the Chinese equivalent is kwan "public servant." Sense of "chief dialect of Chinese" (spoken by officials and educated people and generally in the northern, central, and western provinces and Manchuria) is from c. 1600. Transferred sense of "important person" attested by 1907. The type of small, deep-colored orange so called from 1771, from resemblance of its color to that of robes worn by mandarins.

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advocate (n.)

mid-14c., "one whose profession is to plead cases in a court of justice," a technical term from Roman law, from Old French avocat "barrister, advocate, spokesman," from Latin advocatus "one called to aid (another); a pleader (on one's behalf), advocate," noun use of past participle of advocare "to call (as witness or adviser), summon, invite; call to aid; invoke," from ad "to" (see ad-) + vocare "to call," which is related to vox (genitive vocis) "voice" (from PIE root *wekw- "to speak").

Also in Middle English as "one who intercedes for another," and "protector, champion, patron." Feminine forms advocatess, advocatrice were in use in 15c.; advocatrix is from 17c. Old English glossed Latin advocatus with þingere (see thing).

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