incidental; secondary; accessory
Describes something that is not the main point but accompanies or is attached to the primary matter; often used in formal or technical contexts.
This issue is merely incidental.
The contract has several accessory conditions.
副次的 means 'secondary' or 'subsidiary', often implying a lower rank or importance, whereas 付帯的 simply indicates something is not primary but still attached.
Compound of 付帯 (futai, 'incidental' or 'attached') + 的 (-teki, '-like' or adjectival suffix). 付帯 itself is composed of 付 (fu, 'attach') and 帯 (tai, 'belt' or 'accompany').