Editting en_US.dic file with custom words

Editting en_US.dic file with custom words

I want to manually add words to the en_US.dic library. When I open the
file in a text editor I can add words as needed, but I do not understand
what some of the syntax or attributes are. I spent an hour looking for the
answers but was unable to find what I was looking for.
Here is an example of what I am trying to understand.
logarithm/MS logbook/MS loge/SMNX logged/U loggerhead/SM logger/SM
loggia/SM logging/MS logicality/MS logicalness/M logical/SPY logician/SM
logic/SM login/S
After each of the above words is "/" followed by one or more capital
letters '/SM' or '/U' or '/SPY' etc. and I don't know what they mean and
if I need to use them when I add words manually myself.
Could someone explain this to me?
Thank you for your time.