先史 is read as せんし (senshi) and means prehistory.
せんし
senshi
せんしじだい
prehistoric era
せんしがく
prehistory
せんてんてき
a priori
せんぱん
some time ago
せんどう
guidance
さきぼそり
tapering (to a point)
せんえい
radical
せんぐんせいじ
Songun
せんせいのじゅつ
teachers statement (expounding)
せんどうせい
leadership
せんけんてき
transcendental
せんこうぎじゅつ
prior art (patents)