decline

• n. 下降；後退；傾斜
• vi. 衰える；落ちる；衰退する
• vt. 辞退する；拒否する

de-、down、away。-Clin、曲げる、回す、語源的には lean、incline と同じ、つまり下を向く、ひいては丁重に断る。

decline

decline: [14] The notion underlying decline is of ‘bending away’. It comes via Old French decliner from Latin dēclināre ‘turn aside, go down’, a compound verb formed from the prefix dē-, ‘away, aside’ and clināre ‘bend’, which also produced English incline and recline and is related to lean. Its Latin nominal derivative dēclinātiō has bifurcated in English, to produce declination [14] and, via Old French declinaison, declension [15].

The latter is used only in the specialized grammatical sense ‘set of inflectional endings of a noun’, already present in Latin, which derives from the concept that every inflected form of a word represents a ‘falling away’ from its uninflected base form (the same underlying notion appears in the term oblique case ‘any grammatical sense other than the nominative or vocative’, and indeed the word case itself, whose etymological meaning is ‘fall’; and there are perhaps traces of it in inflection, literally ‘bending’).
=> declension, incline, lean, recline

decline (v.)

late 14c., "to turn aside, deviate," from Old French decliner "to sink, decline, degenerate, turn aside," from Latin declinare "to lower, avoid, deviate, to bend from, inflect," from de- "from" (see de-) + clinare "to bend," from PIE *klei-n-, suffixed form of *klei- "to lean" (see lean (v.)). Sense has been altered since c. 1400 by interpretation of de- as "downward." Meaning "not to consent, politely refuse," is from 1630s. Related: Declined; declining.

decline (n.)

early 14c., "deterioration, degeneration," from Old French declin (see decline (v.)).

1. After years of neglect and decline the city was cleaning itself up.

長年の職務怠慢と不況の後、この町は自己整理を行っている。

2.The electoral fortunes of the Liberal Democratic party may decline .

自由民主党の選挙運が低下する可能性がある。

3.He criticised the government for failing to halt economic decline .

彼は政府が経済の落ち込みを止められなかったと批判した。

4.The decline in marriage has been offset by a rise in cohabitation.

結婚者数の減少は、同居者数の増加によって補われている。

5.I think we can date the decline of Western Civilization quite precisely.

西洋文明が衰退し始めた年代をかなり正確に特定できると思います。