Is it ensure, insure, or assure?
to divide into chapters, put under titles or headings
Latin capitulum 'titles, chapters'
1570s, "to draw up in chapters" (i.e., under "heads"), in part a back-formation from capitulation, in part from Medieval Latin capitulatus, past participle of capitulare "to draw up in heads or chapters, arrange conditions." Often of terms of surrender, hence meaning "to yield on stipulated terms" (1680s). Related: Capitulated; capitulating.