The term "手の込んだ" is described in denshi jisho as being a "Noun or verb acting prenominally".
In the context of Japanese, what does it mean for something to be acting prenominally? For example, does it mean that there's restrictions on where such a word can be used?
In Japanese it is called 連体修飾語 (for a word) or 連体修飾節 (for a phrase). 連体修飾 means modification or description of a noun, or in Japanese 体言に連なる修飾.
As suggested by the word “prenominal”, it is placed before a noun. Eg:
手の込んだ 料理
Here, 手の込んだ is placed before and describes 料理.
Usually, 連体形 of 用言 (動詞, 形容詞 and 形容動詞) is used as 連体修飾語. 手の込んだ is also a 連体形.
手 (名詞) の (助詞) 込ん (連用形 of 動詞 “込む”) だ (連体形 of 助動詞 “た”)
