Beyond the single brivla, a selbri may consist of two brivla placed together. When a selbri is built in this way from more than one brivla, it is called a tanru, a word with no single English equivalent. The nearest analogue to tanru in English are combinations of two nouns such as “lemon tree”. There is no way to tell just by looking at the phrase “lemon tree” exactly what it refers to, even if you know the meanings of “lemon” and “tree” by themselves. As English-speakers, we must simply know that it refers to “a tree which bears lemons as fruits”. A person who didn't know English very well might think of it as analogous to “brown tree” and wonder, “What kind of tree is lemon-colored?”

In Lojban, tanru are also used for the same purposes as English adjective-noun combinations like “big boy” and adverb-verb combinations like “quickly run”. This is a consequence of Lojban not having any such categories as “noun”, “verb”, “adjective”, or “adverb”. English words belonging to any of these categories are translated by simple brivla in Lojban. Here are some examples of tanru:

Note that pelnimre is a lujvo for “lemon”; it is derived from the gismu pelxu, yellow, and nimre, citrus. Note also that sutra can mean “fast/quick” or “quickly” depending on its use:

shows sutra used to translate an adjective, whereas in Example 5.8 it is translating an adverb. (Another correct translation of Example 5.8, however, would be “I am a quick runner”.)

There are special Lojban terms for the two components of a tanru, derived from the place structure of the word tanru. The first component is called the seltau, and the second component is called the tertau.

The most important rule for use in interpreting tanru is that the tertau carries the primary meaning. A pelnimre tricu is primarily a tree, and only secondarily is it connected with lemons in some way. For this reason, an alternative translation of Example 5.6 would be:

This “type of” relationship between the components of a tanru is fundamental to the tanru concept.

We may also say that the seltau modifies the meaning of the tertau:

would be another possible translation of Example 5.6. In the same way, a more explicit translation of Example 5.7 might be:

This “way that boys are big” would be quite different from the way in which elephants are big; big-for-a-boy is small-for-an-elephant.

All tanru are ambiguous semantically. Possible translations of:

include:

In each case the object referred to is a “goer type of table”, but the ambiguous “type of” relationship can mean one of many things. A speaker who uses tanru (and pragmatically all speakers must) takes the risk of being misunderstood. Using tanru is convenient because they are short and expressive; the circumlocution required to squeeze out all ambiguity can require too much effort.

No general theory covering the meaning of all possible tanru exists; probably no such theory can exist. However, some regularities obviously do exist:

are parallel tanru, in the sense that the relationship between barda and prenu is the same as that between cmalu and prenu. Section 5.14 and Section 5.15 contain a partial listing of some types of tanru, with examples.