(adj): of or relating to the theological doctrine of synergism
(adj): working together; used especially of groups, as subsidiaries of a corporation, cooperating for an enhanced effect
(adj): vs. uncooperative) -- (done with or working with others for a common purpose or benefit
Actually, this 'word' belongs not only on the list of words which should be avoided on a first date - it should never be used at all. Especially if you work in a business or corporate setting.
One might think that pharmacologists should be allowed a pass, but they keep using synergism and synergistic in a way that is logically incoherent*.
*: Briefly, the strict definition of synergism involves the notion of local convexity of a particular surface, so it is a local, not a global property. But local convexity is one of those concepts that even mathematicians start to get gnarly about. But think about the shape of the 2-D surface defined by the height of the Rockies as one moves north and east (say) - it will be convex in some places and concave in others. The convexity of Mount Kilimanjaro would presumably be more regularly behaved.
My overall point being that this is a totally skunked term - it has been coopted into meaninglessness by the corpspeak types, but never really had a clear, unambivalent definition to begin with. If your date is impressed by it, find one (a date) with a more demanding mind.