CISC and RISC acronyms used to describe instruction sets were popularized many years after computers following these styles were designed. (A bit like "baroque" or "classical" styles which were named centuries later)
The way computers were designed and the constraints on the instruction sets were quite different when using discrete transistors, LSI, MSI or high integration chips.
One important aspect to understand for the traditional complex CISC instructions is that before the 80's, high performance computers were made of dozens or hundreds of ICs connected together. And the coordination between all these parts was made by microcode.
Microcode allows to create complex sequencing. And that sequencing was necessary because chips were very expensive : The same adder was used for the ALU, for calculating addresses, ... Instructions last many cycles.
So, once you have a lot of microcode in a programmed ROM for sequencing everything in the CPU, the additional cost for adding very complex instructions is low.
Additionally, having complex instructions allows to save some code RAM (and RAM was very expensive), and run faster (microcode accesses were faster than fetching code in RAM).
Contemporary processors try to avoid microcode or reserve it to rarely used instructions. Even for the CISC x86, modern CPUs transform most instructions into 1 or 2 elementary operations.
Some CISC examples : DEC VAX, IBM System 360, Data General Eclipse.
The microcode was sometimes extensible, reprogrammable, or partly in RAM.
Some instructions that were complex in the 70's, as floating point instructions, are now implemented by brute force using huge pipelined multipliers, adders, ... Another example are bit field insertion and extraction instructions which were sequenced and now implemented with barrel shifters.
Obsoleted instructions are those that used complex indirect addressing, function calls with automatic copying of parameters (present in x86 call gates), decimal, ASCII (or other character encoding) instructions, queue/linked list management. Some CPUs even had graphic instructions as bitblt (copy/fill a rectangle) or line drawing directly written in microcode.
Nowadays, the instruction sets of modern RISC CPUs as ARMs or IBM POWER is arguably more complex than ever, and every year new instructions are added, for multimedia, crypto... The difference with traditional CISCs is that they are not designed to be microcoded as a long sequence of calculations or memory accesses.