Unsure why you’re being downvoted, IIRC the original C programmers reference spoke explicitly about how “int” meant the most efficient unit of storage on the target machine.
C’s type naming had real value when it was first designed, at a time when the industry hadn’t yet fully standardised on the 8-bit byte, 32/64-bit words, IEEE floating point, etc.
The fact that “int” could be 16-bits on a PDP-11, 32 on an IBM 370, 36 on a PDP-10 or Honeywell 6000 - that was a real aid for portability in those days.
But nowadays, that’s really historical baggage that causes more problems than it solves, yet we are stuck with it. I think if one was designing C today, one would probably use something like i8,i16,i32,i64,u8,u16,u32,u64,f32,f64,etc instead.
When I write C code, I use stdint.h a lot. I think that’s the best option.
As this paper [0] explains, the initial version of the C compiler for PDP-11 Unix was finished in 1972. And less than a year later (1973), people had ported the C compiler (but not Unix) to Honeywell 6000 series mainframes, and shortly thereafter to IBM 370 series mainframes as well. (Note the text of the paper says "IBM 310" in a couple of places – that's a typo/transcription error for "370".) Both were "larger machines" – the Honeywell 6000 had 36 bit integer arithmetic with 18 bit addressing; the IBM 370 had 32 bit integer arithmetic with 24 bit addressing.
Alan Snyder's 1974 masters thesis [1] describes the Honeywell 6000 GCOS port in some detail. In 1977, there were three different ports of Unix underway – Interdata 7/32 port at Wollongong University in Australia, Interdata 8/32 port at Bell Labs, and IBM 370 mainframe port at Princeton University – and those three had C compilers too.
If you need an 18-bit int it would be called int18 under this scheme. And encountering things like int18 in code, at least you would never wonder what kind of int it was.
The PDP-9, PDP-10, and PDP-18 have 18 bits registers. The world had not settled on 16/32/64 bits at all.
Even the intel 80286 far/fat pointers are 24 bits.