sincere

1、sem-, sin- "one" + cer-(-cerus), from stem/root of crescere "grow" + -e.
2、字面含义："of one growth" (i.e. "not hybrid, unmixed").

sincere (adj.)

1530s, "pure, unmixed," from Middle French sincere (16c.), from Latin sincerus, of things, "whole, clean, pure, uninjured, unmixed," figuratively "sound, genuine, pure, true, candid, truthful," of uncertain origin. Ground sense seems to be "that which is not falsified." Meaning "free from pretense or falsehood" in English is from 1530s.

There has been a temptation to see the first element as Latin sine "without." But there is no etymological justification for the common story that the word means "without wax" (*sin cerae), which is dismissed out of hand by OED and others, and the stories invented to justify that folk etymology are even less plausible. Watkins has it as originally "of one growth" (i.e. "not hybrid, unmixed"), from PIE *sm-ke-ro-, from *sem- "one" (see same) + root of crescere "to grow" (see crescent).

1. I got this phone call from a gentleman, who seemed sincere enough.

这个电话是一位绅士打来的，他似乎非常诚恳。

2. Sincere performances and gritty Boston settings add to the film's realism.

真诚的表演和对波士顿这一背景城市的真实刻画增添了电影的现实主义色彩。

3. All the well-meant, sincere advice is largely wasted on him.

他对所有善意、真挚的建议基本都无动于衷。

4. There was a sincere expression of friendliness on both their faces.

他们俩的脸上都流露出真挚友好的表情。

5. Primo de Rivera himself was a benevolent and sincere paternalist.

普里莫·德里韦拉本人是个仁慈而真诚的家长式人物。

【open, frank, sincere, blunt, honest, plain, straightforward】
这组词都有“坦率，诚实”的意思，其区别是：
open: 指不隐瞒自己的秘密，愿意向他人表露自己或公开暴露自己的缺点。
frank: 强调毫无保留地畅所欲言，不受任何约束。
sincere: 侧重指一个人出自内心地对某人某事表示一种诚意。
blunt: 指讲话坦白直率、不客气，但隐含不得体、不顾及他人感情等意味。
honest: 指遵守正直等道德准则。
plain: 指直言不讳，毫不做作或故弄玄虚。
straightforward: 多用于答复、叙述等场合。指直截了当，不回避，或故弄玄虚。