Etymology
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adhere (v.)

1590s, from French adhérer "to stick, adhere" (15c., corrected from earlier aderer, 14c.) or directly from Latin adhaerare "to stick, cling to," from ad "to" (see ad-) + haerere "to stick" (see hesitation). Originally often of persons, "to cleave to a leader, cause, party, etc." (compare adherent (n.), which still often retains this sense). Related: Adhered; adhering.

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adherence (n.)

mid-15c., "steady attachment of the mind or feelings to a person, cause, belief, etc.," from Old French adhérence, from Medieval Latin adhaerentia, abstract noun from Latin adhaerent-, present participle stem of adhaerare "stick to," from ad "to" (see ad-) + haerere "to stick" (see hesitation). Rare in a physical sense, adhesion being the usual word for that.

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adherent (adj.)

late 14c., "sticking, clinging to, adhesive," from Old French adherent or directly from Latin adhaerentem (nominative adhaerens), present participle of adhaerere "stick to," from ad "to" (see ad-) + haerere "to stick" (see hesitation).

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adherent (n.)

early 15c., "follower, supporter, one who upholds (a leader, cause, etc.)," from Old French adherent or directly from Latin adhaerentem (nominative adhaerens), present participle of adhaerere "stick to," from ad "to" (see ad-) + haerere "to stick" (see hesitation). Meaning "adhesive substance" is from 1912.

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adhesion (n.)
Origin and meaning of adhesion

1620s, "act or state of sticking or being stuck, a being united or attached," from French adhésion or directly from Latin adhaesionem (nominative adhaesio) "a sticking to," noun of action from past-participle stem of adhaerare "to stick to, cling to," from ad "to" (see ad-) + haerere "to stick" (see hesitation). The earliest English use is of persons ("faith is adhesion unto God"), but by 18c. adhesion was "generally used in the material, and adherence in the metaphysical sense." [Johnson]

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adhesive (adj.)

"sticky, cleaving or clinging," 1660s, from French adhésif, formed in French from Latin adhaes-, past-participle stem of adhaerere "stick to" (see adherent (adj.)).

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adhesive (n.)

1881, from adhesive (adj.). Originally of postage stamps, short for adhesive stamp (1840). By 1900 as "a substance that causes to adhere."

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adiabatic (adj.)

"without transference, impossible (to heat)," 1838, with -ic + Greek adiabatos "not to be passed" (of rivers, etc.), from a- "not" (see a- (3)) + diabatos "to be crossed or passed, fordable," from dia "through" (see dia-) + batos "passable," from bainein "to go, walk, step" (from PIE root *gwa- "to go, come"). In thermodynamics, of a change in volume without change in heat.

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adiaphorous (adj.)

"indifferent, non-essential, morally neither right nor wrong," 1630s, from Greek adiaphoros "not different; indifferent," from a- "not" (see a- (3)) + diaphoros "different."

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adieu (interj.)

late 14c., adewe, from Old French a Dieu, a Deu, shortened from phrases such as a dieu (vous) commant "I commend (you) to God," from a "to" (see ad-) + dieu "God," from Latin deum, accusative of deus "god" (from PIE *deiwos "god" (from root *dyeu- "to shine").

Originally it was said to the party left (farewell was to the party setting forth), but in English it came to be used as a general parting salutation. As a noun, "expression of kind wishes upon departure," late 14c. Compare the native parting salutation good-bye, a contraction of God be with ye.

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