I would say that an adiabatic lapse rate is indeed synonymous with convection, though what is not known when you just say there is convection is the turnover timescale. The timescale could be so long that it wouldn't look much like convection, but then, that can happen in convective atmospheres like that of the Sun-- in some layers, the convection can be so slow you wouldn't notice it on a sound crossing time across the scale of gradients. But the reason I'm claiming they are synonymous is that convection is about the only reason you can think of why there would be an adiabatic lapse rate for the overall gradient in the atmosphere.
The way adiabatic convection works is, you can think of every parcel of gas in the convective region as if it was the same parcel, just found at a different time. In short, every parcel goes everywhere eventually. What's more, as the parcel goes everywhere, it remains insulated, so it's just the same parcel expanding and contracting with no heat exchange. That's what sets the adiabatic gradient everywhere. Another way to say that is, the entropy per gram is the same everywhere, because entropy doesn't change if there is no heat transport, and if the entropy of each parcel stays the same, and if each parcel goes everywhere, then the entropy per gram is constant everywhere. That's what an adiabatic lapse rate means.
Now, if there is not convection, so parcels just stay put, how would they know to have the same entropy as each other? So it is generally convection that induces an adiabatic lapse rate, though the convection could still be rather slow if the heat transport rate is also very slow.
No doubt there are complications I am leaving out, like what happens when there are changes in ionization or phase which alter what we mean by the adiabatic lapse rate, so I'm just talking about the simplest situation where we are not considering such details. We are basically assuming the parcel is always in thermodynamic equilibrium, even though its environment is slowly changing.