Joining the thread a bit late since I have just discovered it.

There are, as you might well guess - several spellings of SEGOTIA - including SAGOSHA and SHEGOSHIA.   As everyone has said its meaning is "close friend" in male usage. Used in "The Hair of the Dogma" by Myles na gCopaleen.   A dictionary of Irish Slang "SLANGUAGE" by Bernard Share, 2nd edition published in 2003 by Giles and McMillan - which has its own web site.