I would say that bonds are very similar to derivatives. The first reason is that the value of a bond depends on (i. e. derives from) the market rates curve. And the second reason is that every bond has a maturity date. By the way, bond math and option math have the comparable complexity, and I think that bonds look more 'derivatively' than, say, futures. Then let's take exchange traded notes which look more like structured products than ETF shares. And they have exact maturity dates.

There is one more thing. When stock or FX traders talk about market timing they simply mean market risk, because they don't need to worry about expiry or maturity dates in such instruments. And the guys who trade term contracts must keep in mind a Latin phrase 'Memento mori', because the time to contract death affects the price. This actually means that it's better to divide the realm of tradeable instruments into term contracts and literally immortal securities, than to talk about underliers and derivatives.