In the githyanki language, apostrophes (which are not pronounced)
separate different morphemes which have been combined into a single
word. For example, gish'sarath combines the word gish, or "skilled,"
with sarath, or "sergeant." Githyanki who have trained with great
heroes add the prefix gi' ("student of") to their trainer's name.
– Githyanki, from Wikipedia
Also from the very same source:
The githyanki captain, the gish githyanki, and the githyanki soldier
appeared in Monster Manual IV (2006).
The gith races are truly efficient warriors in that they combine all
disciplines in their tactics; it is probably the case that the only
race to even approach this multi-disciplinary approach to combat is
humanity itself. The githyanki, arguably the most aggressive of the
gith races, combine magic, psionics and swordplay in a single,
terrifying wave of assault. The most significant example of this can
be found in the gish, students of both the magic word and the magic
– planewalker.com: the gish (2005)
Planewalker.com is/was/has been a semi-official website - meaning: "while WotC isn't working with the setting we have the nod to go ahead in development" (from their FAQ) - dedicated to the Planescape setting, and it was established in 1999 by Brannon Hollingsworth, according to their FAQ. Their info seems pretty reliable, though I'm not entirely sure about its current validity. The material on the "gish" seems solid, though.
All emphases mine.