anesthesiology (n.)

1721, "loss of feeling," medical Latin, from Greek anaisthēsia "want of feeling or perception, lack of sensation (to pleasure or pain)," abstract noun from an- "without" (see an- (1)) + aisthēsis "feeling" (from PIE root *au- "to perceive"). For the abstract noun ending, see -ia.

As "a procedure for the prevention of pain in surgical operations," attested from 1846. Aesthesia "capacity for feeling" is attested in English from 1853, perhaps a back-formation.

word-forming element indicating "branch of knowledge, science," now the usual form of -logy. Originally used c. 1800 in nonce formations (commonsensology, etc.), it gained legitimacy by influence of the proper formation in geology, mythology, etc., where the -o- is a stem vowel in the previous element.

The second element is prop[erly] -logy (-logue, etc.), the -o- belonging to the preceding element; but the accent makes the apparent element in E[nglish] to be -ology, which is hence often used as an independent word. [Century Dictionary]