noun-modifying (irregular)
systematic; methodical; organized
Describes something done or arranged according to a clear system or method; often used for research, thinking, or procedures.
彼は系統だった方法で問題を分析した。
He analyzed the problem in a systematic way.
系統だった勉強をすれば、もっと早く上達する。
If you study in an organized manner, you'll improve faster.
From the past tense of the verb 系統立つ (to be systematic), used as a prenominal adjective. The kanji 系統 means 'system' or 'lineage', and 立つ here contributes the sense of 'standing' or 'being established'.