specifying a non-momentary switch?
I've always assumed the opposite of "momentary" was "toggle". The wikipedia entry appears to confirm this:


  The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. Each set of contacts can be in one of two states: either "closed" meaning the contacts are touching and electricity can flow between them, or "open", meaning the contacts are separated and the switch is nonconducting. The mechanism actuating the transition between these two states (open or closed) can be either a "toggle" (flip switch for continuous "on" or "off") or "momentary" (push-for "on" or push-for "off") type.


But a quick websearch seems to show that there are some switches sold as momentary toggles, so I'm not sure there is a completely unambiguous term.