A compound word is often composed of two or three morphemes. According to L¨u (1984), 61% of the 3,000 most commonly used Chinese words are disyllabic. Morphemes in compound words can be separated into two categories: free morpheme (represented by Root beginning with a capital R) and bound morpheme (represented by root beginning with a small letter r). A free morpheme or unbound morpheme is one that can stand alone or can appear with other morphemes; a bound morpheme is a morpheme (the most basic unit of meaning) that can appear only as part of a larger word.
Here are several examples of compound words composed of Root and root:
root–root type:
蘑菇(m´og¯u mushroom-mushroom “mushroom”)
討論(t˘ao-l`un discuss-discuss “to discuss”)
Root–Root type:
馬路(m˘a-l`u horse-road “road”)
借用(ji`e-y`ong borrow-use “to borrow”)
root–Root type:
觸角(ch`u-ji˘ao touch-horn “(insect) antenna”)
購買(g`ou-m˘ai buy-buy “to buy”)
Root–root type:
賭博(dˇu-j`u gamble-utensil “gambling equipment”)
幫助(b¯ang-zh`u help-assist “help”)
Reference: Chinese: a linguistic introduction by Chao Fen Sun
