decasyllabic
adjective
deca·syl·lab·ic ˌde-kə-sə-ˈla-bik 
: consisting of 10 syllables or composed of verses of 10 syllables
decasyllabic noun
decasyllable
ˈde-kə-ˌsi-lə-bəl
noun ˌde-kə-ˈsi-
Word History
Etymology
probably from French décasyllabique, from Greek dekasyllabos, from deka- deca- + syllabē syllable
First Known Use
1771, in the meaning defined above