(n.) Something placed in a book to guide in finding a particular page or passage; also, a label in a book to designate the owner; a bookplate.

abode area bearings bookmark cairn cardinal point catstone chief thing climax core cornerstone crisis critical point crux district emplacement essence essential essential matter fundamental gist gravamen great point heart high point hole important thing issue kernel keystone landmark latitude and longitude lieu lighthouse lightship locale locality location locus main point main thing mark marker material point meat menhir milepost milestone monument nub pharos pinpoint pith pivot place placement platform point position real issue region salient point seamark sine qua non site situation situs spot stead substance substantive point the bottom line the point tower turning point watchtower whereabout whereabouts