occur

oc-,相对，对着的，-cur,跑，词源同current,course.即跑到一起的，引申词义遇到，出现，发生。

occur

occur: [16] Etymologically, occur means ‘run towards’. It was borrowed from Latin occurrere, a compound verb formed from the prefix ob- ‘towards’ and currere ‘run’ (source of English course, current, etc). This had the sense ‘run to meet’, hence simply ‘meet’, which survived into English: ‘The whole multitude might freely move … with very little occurring or interfering’, Richard Bentley, Boyle Lectures 1692. But ‘meeting’ also passed into ‘presenting itself’, ‘appearing’, and hence ‘happening’ – from which the main present-day meaning of English occur comes.
=> course, current

occur (v.)

1520s, "meet, meet in argument," from Middle French occurrer "happen unexpectedly" or directly from Latin occurrere "run to meet, run against, befall, present itself," from ob "against, toward" (see ob-) + currere "to run" (see current (adj.)). Sense development is from "meet" to "present itself" to "appear" to "happen" ("present itself in the course of events"). Meaning "to come into one's mind" is from 1620s. Related: Occurred; occurring.

1. If these drugs are stopped abruptly then some withdrawal symptoms may occur.

如果突然停服这些药，则可能出现一些戒断症状。

2. Keep a pad handy to jot down queries as they occur.

手边放一本便笺簿，以便有问题时随时记下。

3. Nitrates are chemicals that occur naturally in water and the soil.

硝酸盐是水和土壤中自然存在的化学物质。

4. Emergency cooling systems could fail and a reactor meltdown could occur.

紧急冷却系统有可能失灵，核反应堆有可能发生堆芯熔毁。

5. Unless you respect other people's religions, horrible mistakes and conflict will occur.

如果不尊重别人的宗教信仰，就会祷下大错，酿成冲突。