Thayer's Greek Lexicon

 Siloam = "sent"
1. the Pool of Siloam, a fountain of water in Jerusalem, also called
Shiloah in Isa. 8:6
2. the Tower of Siloam, may have been a tower near or over the
Pool of Siloam, which fell down killing 18 men; very likely
they were purifying themselves. (Gill)