[sub- + chapter]sub- is a prefix occurring originally in loanwords from Latin (subject; subtract; subvert; subsidy). On this model, sub- is freely attached to elements of any origin and used with the meaning “under,” “below,”“beneath” (subalpine; substratum), “slightly,” “imperfectly,” “nearly” (subcolumnar; subtropical), “secondary,” “subordinate” (subcommittee; subplot)