Man pages matching name thread in section 3tcl:

thread.3tcl.en	debian 10 / tcl-thread
Thread.3tcl.en	debian 10 / tcl8.6-doc
thread.3tcl.en	debian 11 / tcl-thread
Thread.3tcl.en	debian 11 / tcl8.6-doc
thread.3tcl.en	debian 12 / tcl-thread
Thread.3tcl.en	debian 12 / tcl8.6-doc