atactic
adjective
atac·tic (ˌ)ā-ˈtak-tik 
: of, relating to, or being a polymer exhibiting no stereochemical regularity of structure
atactic polypropylene
compare isotactic 
Word History
Etymology
International Scientific Vocabulary a- entry 2 + -tactic
First Known Use
1957, in the meaning defined above
Medical Definition
atactic
adjective
atac·tic (ˈ)ā-ˈtak-tik
: lacking regularity or coordination
specifically : characterized by ataxia