Regular, having a definite principle, methodical.

Of an action, pursuit, procedure, etc.: characterized by method or order; performed or carried on systematically or meticulously. Of discourse, etc…

Of an action, pursuit, discourse, etc.: characterized by method or order; = methodical, adj. 1a; relating to method. Also (occasionally) of a person…

gen. = systematic, adj. 4a.

Arranged or conducted according to a system, plan, or organized method; involving or observing a system; (of a person) acting according to system…

= systematic, adj. (in various senses).

In extended use: systematic, methodical, meticulous.