antiparallel
adjective
an·ti·par·al·lel 
ˌan-tē-ˈper-ə-ˌlel,
ˌan-ˌtī- -ləl
: parallel but oppositely directed or oriented
antiparallel electron spins
two antiparallel chains of nucleotides comprise DNA
Word History
First Known Use
circa 1660, in the meaning defined above
Medical Definition
antiparallel
adjective
an·ti·par·al·lel ˌant-i-ˈpar-ə-ˌlel, ˌan-ˌtī-, -ləl
: parallel but oppositely directed or oriented
two antiparallel chains of nucleotides comprise DNA