Thing, thingy, whatsit.
The universal French placeholder for any object or concept whose name escapes you. "Machin" and "bidule" do the same job. Absolutely everywhere in spoken French.
Venezuela and the DR say "vaina" for exactly this job.
Reading a definition isn't the same as saying it to someone. Lingo Kaiava is a voice tutor set to French — it uses truc the way locals do, corrects you in the moment, and never "fixes" the way real people actually talk into textbook French.
Free to start. No signup for your first conversation.