The clock enable bits in RCC_AxBxENR registers have a neame, which usually follows a easily understandable pattern: name of the peripheral, followed by EN suffix. For example, the enable bit for SPI2 is called SPI2EN. This allows to use the enable bits even without looking them up in the RM.

However, ST sometimes departs from this scheme, and uses a strange name for some peripherals. Often, the name is "normal" in some families, and "strange" in others, for the same peripheral. Here are some examples:

• FLASH interface enable bit is called FLASHEN in 'C0/'G0/'G4/'L4/'L5/'U5, FLITFEN in 'F0/'F1/'F3/'L1 and, wait for it, MIFEN in 'L0. There is no "normal" FLASH interface enable bit in some families, but they still have the low-power variant of it: in 'H7 it's called FLASHLPEN and in 'F4/'F7 it's called FLITFLPEN.
• GPIOx clock enable bit is called IOPxEN in 'F1, which has a very different GPIO from other families and GPIO is on APB bus. In most of other STM32 families, GPIO are on AHB bus and the enable bits are called GPIOxEN; however, with the inexplicable exception of 'F0/'F3 families, where they are called IOPxEN as in 'F1. To increase confusion, the CMSIS-mandated headers for 'F0/'F3 don't use the IOPxEN notation for these bits, but the "usual" GPIOxEN one.
  In STM32 families based on Cortex-M0+, where GPIO are not connected through the mcu's bus fabric but are on the processor's private IO bus (and consequently the enable bits are in a separate RCC_IOPENR register), the picture is a mixed one again: in 'G0/'C0, the enable bits are still called GPIOxEN, but in 'L0, they are called IOPxEN, and called so in the CMSIS-mandated header, too, although with defined aliases to the "more usual" GPIOxEN...
  What a mess.
• In most STM32, RTC's APB interface is always enabled, but some STM32 have it behind a switch. The related enable bit is called alternatively RTCAPBEN and RTCEN in various STM32 models.
• The bit enabling SYSCFG (and in some STM32 models simultaneously enabling also other peripherals) is called in most cases SYSCFGEN, but in 'F0 it's called SYSCFGCOMPEN.