subsidiarily

Subsidiarily is an adverb that denotes a secondary or subsidiary basis or manner. Derived from the adjective subsidiary, it belongs to formal or technical language and is used to indicate that something applies only as a fallback or auxiliary option, rather than as the primary rule. The word ultimately traces to Latin subsidium, meaning aid or support.

In legal writing, subsidiarily describes secondary liability or alternative remedies. For example, a party may be subsidiarily liable for a debt, meaning liability arises if the primary debtor fails to pay. Contracts may provide that a remedy is available subsidiarily, signaling that the main remedy must be exhausted before the secondary one can be invoked. In statutory and regulatory contexts, subsidiarily applicable rules may apply only to matters not governed by a primary regime.

Outside law, subsidiarily can appear in analytical or policy discussions to indicate that an argument or effect is secondary to the main consideration. The usage is most common in European legal drafting and international arbitration, but can appear in academic prose more broadly.

Related terms include subsidiary, subsidiarity, and secondary liability.