I do take your point, though. I see the wiki also uses the terms "thick" and "thin" clients to refer to full nodes and non full node wallets respectively, although that's not a term I've ever seen used elsewhere. I do think it is less confusing for everyone not to refer to non full nodes as clients at all though, and just refer to them as wallets, since that's what they are.
i don't like the terms "think" and "thin" either.
but for client i find it OK to describe all types including full node and SPV nodes. the actual definition of a "client" in "computing" is simply
a computer or a software that connects to another remote computer and uses its resources.in fact with this definition it may not be completely correct to call a full node, a client because when you run a full node there is no longer a "server-client" relationship, it is all "peer to peer" (indicating equality) whereas when using other types such as SPV there is no longer any equality, the "client" (SPV node) relies on the "server" (Full node).
here is wikipedia (also has thin and thick definitions):
https://en.wikipedia.org/wiki/Client_(computing)