KSI

Killed or Seriously Injured.

Ksi

[Cyrillic] Ksi (Ѯ, ѯ) is a letter of the early Cyrillic alphabet, derived from the Greek letter Xi (Ξ, ξ). It was mainly used in Greek loanwords, especially words relating to the Church. Ksi was eliminated from the Russian alphabet along with psi, omega, and yus in the Civil Script of 1708 (Peter the Great`s Grazhdanka), and has also be...
Found on http://en.wikipedia.org/wiki/Ksi_(Cyrillic)

KSI

Killed or Seriously Injured
Found on https://www.encyclo.co.uk/local/21417

Ksi

kilopounds per square inch (a unit of stress).
Found on http://www.textilesintelligence.com/glo/index.cfm?SECTION=K
No exact match found