applicate comes from Latin applicatus, past participle of applicare ('to attach, apply'), from ad- ('to') and plicare ('to fold'). The formation turns on ad-, a prefixal element preserved in the word's surface shape and tied to the older base described in its history. In modern use, the adjective sense is "applied or put to a particular use; in geometry, an applied ordinate", which keeps the etymology connected to the word's present dictionary value rather than treating it as a merely historical label. The wider word family includes related English forms such as apply, application, applicable, applicant, showing how the same base continues to support neighboring English vocabulary. The principal historical forms in the chain include Latin applicatus, Latin ad-, Latin plicare, Proto-Indo-European *plek-, which anchor the explanation in named linguistic material.