連体 is an abbreviation often seen in part-of-speech labels in dictionaries.
Words like この and 大きな are classified as rentaishi and used as adnominal modifiers.
attributive form
genitive case; adnominal case
pre-noun adjectival; adnominal adjective
adnominal modifier; modifier of a non-inflectable word
A grammatical term formed from 連 “connect” and 体, referring to 体言 such as nouns. It denotes a form’s attributive connection to a following noun or other nominal expression.