What does the prefix ob- mean?
Ob- comes from the Latin ob, which means "against", "facing", "in the way of" or "toward". It shows opposition, blocking or direction toward something.
ESEN
Prefix · direction · against/toward
ob-
Means "against," "in the way," or "toward": object, observe, obtain, obvious, obstacle, obscure.
Basic
Written by Bryan López, English teacher · Updated
Ob- also hides itself
Like ad-, the prefix ob- changes to match the letter that comes next. Before c it becomes oc-, before f it becomes of- and before p it becomes op-. That is why many words that start with oc-, of- or op- actually have a hidden ob-. If you know this, you will recognize new words much more easily.
How it is used
Assimilates to the following consonant, producing several surface forms:
- ob- (base form)ject → objectserve → observetain → obtainvious → obviousstacle → obstaclescure → obscure
- assimilated: oc-/of-/op-cur → occurcasion → occasionfer → offerfend → offendpose → opposeportunity → opportunity
Pronunciation: /ɒb/ (stressed) or /əb/ (unstressed). Assimilated forms: oc- (occur), of- (offer, offend), op- (oppose, opportunity).
How it is pronounced
ob-/ɒb/ /əb/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Examples
Root word
With ob-
In a phrase
- jectobjectSeveral board members will object to the proposed budget cuts.
- serveobserveScientists observe the stars through powerful telescopes at night.
- tainobtainIt is difficult to obtain a visa without a valid sponsor.
- viousobviousThe solution was obvious once she looked at the problem differently.
- stacleobstacleThe biggest obstacle to her success was a lack of funding.
- scureobscureThe artist remained obscure for decades before being finally recognised.
- structobstructA fallen tree obstructed the road and caused long delays.
Common mistakes
"occur," "offer," and "oppose" have no prefix
oc-, of-, op- are assimilated forms of ob-: occur (ob+cur), offer (ob+fer), oppose (ob+pose), opportunity (ob+portunity)
Just as ad- assimilates in affect (ad+fect) and arrive (ad+rive), ob- assimilates before certain consonants: ob + cur = occur (b → c), ob + fer = offer (b → f), ob + pose = oppose (b → p). The double consonant at the start of the base word is the assimilation signal. Recognising these hidden ob- words reveals their meaning: occur = run against/into; oppose = place against; opportunity = a favourable approach.
A trick to remember it
Picture something planted right in your path, blocking you: ob- = against, in the way. obstacle, object.
Practise what you learned
Exercise 1 · Form the word
Exercise 2 · Pick the right one
Which word hides assimilated ob- inside it?
Frequently asked questions
What does the prefix ob- mean in English?
The prefix ob- means "against," "in the way," or "toward": object, observe, obtain, obvious, obstacle, obscure.
How do you pronounce ob-?
The prefix ob- is pronounced /ɒb/ /əb/. For example, "object".
Can you give an example of a word with ob-?
"ject" becomes "object". It is a typical example of the ob- prefix.
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