First opened Sunday, December 27, 2009
恐らく
おそらく
- middle-high (nakadaka): falls after mora 2
How to read it: a line over a kana means the voice is high there, and ↓ marks where it drops. A kana with no line is low. With no ↓ the pitch stays high to the end and does not drop even on a following particle (が, は).
perhaps
“Perhaps” is a clipped phrase whose first half is still being argued over.
Taken apart
No breakdown is shown for this word: the only split Wiktionary offers is hedged (see the marked line below), and it doesn't spell the word — it describes where the sound may come from — so showing it as the word's parts would be a guess.
Written with 恐
In a sentence
彼はおそらく来るだろう。
He is likely to come.
恐らく明日は晴れでしょう。
It will be fine weather tomorrow, perhaps.
Sentences are from Tatoeba (CC BY 2.0 FR), picked by fixed rules from a dated export and shown unchanged. Nobody has reviewed them one by one.
What Wiktionary says
Quoted line by line from Wiktionary's Etymology section for this reading, taken from one dated dump so it can't change underneath us. Nothing below is paraphrased.
Not settled
Wiktionary itself hedges on part of this word's origin — those lines are marked below.
- Hedged“Sources are agreed that modern osoraku as an adverb is a clipping of older noun phrase 恐らくは (osoraku wa), trimming off the topic particle は (wa). This clipped form first appears in the late 1500s. Speculatively, this usage might have been influenced by the -ku adverbial ending used for adjectives.”
- “Past there, different sources give different derivations for the osoraku portion itself.”
- Hedged“* May be from the -ku nominalization of verb 恐る (osoru, “to fear, to be afraid of”), originally a 四段活用 (yodan katsuyō, “quadrigrade-conjugation”) verb. In the traditional analysis, the く (ku) noun-forming suffix attaches to the 未然形 (mizenkei, “irrealis form”) of the verb stem, ending in -a: osoru (plain form) → osora- (irrealis) + -ku (noun-forming suffix) = osoraku.”
- Hedged“* Older documents also record a form 恐るらくは (osoruraku wa), which may be from 恐る (osoru, “to fear, to be afraid of”) as either a 上二段活用 (kami nidan katsuyō, “upper bigrade-conjugation”) or 下二段活用 (shimo nidan katsuyō, “lower bigrade-conjugation”) verb. In the traditional analysis, for bigrade verbs, the く (ku) noun-forming suffix manifests instead as らく (raku) and attaches to the 終止形 (shūshikei, “terminal or predicative form”) of the verb, the standard "plain" or "dictionary form" ending in -u: osoru + -raku = osoruraku.”
- “The irregularities in the verb form required for -ku nominalization, and the shifts between bare -ku and longer form -raku, can be resolved if the underlying form of the nominalizing suffix were -aku instead, syntactically acting as a noun, and thus requiring that the verb be in the 連体形 (rentaikei, “adnominal form”). Also, Old Japanese did not allow hiatus (consecutive vowels without an intervening consonant), forcing either vowel fusion or vowel elision. For bigrade osoru, we would have adnominal form osoruru + suffix -aku, with the final -u in osoruru eliding to give us attested osoruraku.”
- “*/osoruru aku wa/ → /osoruraku wa/ → /osoraku wa/ → /osoraku/”
Source: Wiktionary: 恐らく (dump of 2026-09-02), available under CC BY-SA 4.0. Reading, meaning and part of speech from JMdict, and kanji readings from KANJIDIC2 (EDRDG).
What the labels mean
- 和語 Native Japanese
- Words that were already Japanese before Chinese vocabulary arrived — usually written with kun'yomi and often short.
- Derivation
- A word built from a stem plus a suffix or prefix.
- Clipping
- A longer word or phrase shortened in everyday use.
- Sound change
- The pronunciation shifted over the centuries.