Apostrophe instead of an O-ending
The final O of a noun can be omitted. In that case, an apostrophe is written instead of O. However, it is only possible to omit the O ending when it is not followed by the J or N endings. In speech, the accent stays on the same syllable as usual, as if the O were still present:
- turmento → turment' (turmEnt')
- historio → histori' (historI')
- metroo → metro' (metrO').
- ĉielo → ĉiel' (ĉiEl').
It is not possible to use an apostrophe instead of an A-ending, E-ending or verb ending. Note that it is also not possible to use an apostrophe instead of the endings ON, OJ and OJN. Har' always means haro (hair), never haron, haroj (hairs) or harojn.
For some table words ending in O, the final vowel "o" isn't a real O-ending, so those can't be replaced with apostrophes. It isn't possible, then, to use ki', ti', i', ĉi', neni' instead of kio, tio, io, ĉio, nenio.
Apostrophe with la
The vowel "a" in the definite article la can be left out and replaced by an apostrophe. → l'. This short form is preferable only used after a prepositon that ends in a vowel: ĉe l', tra l', pro l':
- Liberigu nin Dio, de l' sovaĝaj Normandoj! - Deliver us oh God from the savage Normans!
Note that l' is written as an independent word: de l' maro (not de l'maro', nor del' maro).
Mainly in poetry
Apostrophes are used in poetry mainly to avoid overuse of vowels.
Post longa migrado sur dorna la voj'
Minacis nin ondoj de l' maro;
Sed venkis ni ilin kaj velas kun ĝoj'
Al verda haven' de l' homaro.
Post longa batalo, maldolĉa turment'
La stela standardo jam flirtas en vent'.
In ordinary language, apostrophes are very uncommon. In the spoken language, the apostrophe is rarely used at all as described here, for the abbreviation of words.
Dank' al
An apostrophe is also traditionally used in the expression dank' al (thanks to...), which shows the cause of something favorable, = "pro la (favora) influo de" ("due to the [favorable] influence of"). Dank' al appears in every register of use of the language, also in spoken form:
- Jes, dank' al Dio, ĉio estas en bona ordo. - Yes, thank God, everything is in good order.
- Dank' al lia instruado mi sukcesis en la ekzameno. - Thanks to his teaching I passed the exam.
The expression danke al can be used with the same meaning.
Un'
When beats, rhythms, etc. are counted, an apostrophe form of the numeral unu (one) can also be used.
- Un'! du! un'! du! — La soldatoj marŝis. = Unu! du!... - One! Two! One! Two! — The soldiers marched.
- "Un', du, tri, kvar", li kalkulis laŭte. = Unu, du... - "One, two, three, four", he counted aloud.
Un' can only appear in independent form, as for use as an interjection, like in the examples above. It can't appear in ordinary sentences. It isn't possible to say, for example: Mi havas nur un' amikon. The only correct form is: Mi havas nur unu amikon. (I have only one friend)