# Any systematic way of building different adjectives from numerals than just ordinals?

I can imagine quite a few adjectives related to some small numbers at least, mostly by how they work in my native language (there will presumably be many more). For example with 2 (derived from dva – two, druhý – second, or dvojka – the digit two):

• dvojný (dual, double in nature): dvojná vazba (double bond), dvojné číslo (dual grammatical number)
• dvojitý (double in count, duplicate): dvojitý vrchol (double peak), dvojité béčko (double flat accidental)
• dvojí (twofold) as in The importance of this discovery is twofold: ...
• dvojkový (binary): dvojková soustava (binary numeral system)
• druhotný (secondary): druhotná obava (secondary concern), druhotný přízvuk (secondary stress)

With the exception of the latter, they all are used (with rapidly decreasing frequency, of course) also with 3, 4, etc. And the latter does work in English so there's no fundamental reason for it to be exceptional either. Yet in Duolingo, I have only learnt of adding -a to form ordinal numerals (first, second, ...) as if that was the only adjective paradigm I could ever want to use with numbers.

I have tried to look up some in ESPDIC but found binara or duala (which might or might not come from du but feels more like a direct loanword and I have my doubts that -al- would work with other roots). It's still possible that these are just inventions of people who used a familiar root borrowed from another language and did not try hard enough to find a “native” Esperanto affix that would do the same. Are there any? I would find it very strange, especially for Czech, if there was a niche in which it was so much more regular than Esperanto.

• Can you please add some examples of the words you listed with a sentence or two (in Czech and/or English)? That would help to better understand the difference in their meaning. Oct 25, 2016 at 10:54
• Sure, good idea. I added some phrases and one sentence. Oct 25, 2016 at 11:15

Here is what I managed to find in PIV and Tekstaro:

• duopa (dvojný):

duopa flava linio karakteriza de natrio ĉe spektroskopo

For double grammatical number Wikipedia has dunombro (I do not know how proper is this).

• duobla (dvojitý kaj dvojí):

por ĉiu tago mi ricevas kvin frankojn, sed por la hodiaŭa tago mi ricevis duoblan pagon, t.e. dek frankojn

• duuma (dvojkový):

en la duuma sistemo, 4, 7 k 9 estas skribataj respektive 100, 111 k 1001.

…prezentitaj ne nur la ĉefaj herooj, sed ankaŭ la duagradaj.

However, as usual, it depends on the particular sentence and there might be better words in specific cases.

Bonvolu korekti min, se mi eraras.

• What wonderful resources! I'm very new here, I didn't know these sites. Next time I'll know where to look first to do my research. Oct 25, 2016 at 12:32
• Another suffix is -tet-, e.g. duteto, triteto, dekduteto (musical duet, trio, duodecet). Oct 25, 2016 at 12:46
• -tet- is not an official affix, but one of the many proposed affixes.
– 2_K_
Oct 27, 2016 at 7:52

There are many other suffixes that can be used with ordinals like "two":

• duono - half
• duope - in groups of two
• dufoje - twice
• duafoje - for the second time
• duoblo - double
• Thanks! Are there more options for adjectives specifically, though? Oct 25, 2016 at 11:16
• All of these can be used with other numbers and freely turned into adjectives, adverbs, and prefixes: deksepobleco (17-fold-ness), centunuope (in groups of 101), kvindekkvinonigita (divided by 55), etc. Oct 25, 2016 at 12:43
• somehow I totally missed the 'adjective' part of the question :D I hope the answer helps others anyway! Oct 26, 2016 at 0:49