tachyphylaxis

UK: /ˌtækɪfɪˈlæksɪs/ US: (tak′ə fi lak′sis)

WordReference Random House Unabridged Dictionary of American English © 2025

tach•y•phy•lax•is  (tak′ə fi lak′sis), n. 

1. Medicine immediate, temporary immunization against the effects of injection of a toxic extract owing to previous small injections of the same extract.

a decreased response to a medicine given over a period of time so that larger doses are required to produce the same response. Also, tach•y•phy•lax•i•a  (tak′ə fi lak′sē ə). 

• tachy- + Greek phýlaxis a guarding, equivalent. to phylak- (stem of phylássein to guard) + -sis -sis

tach•y•phy•lac•tic  (tak′ə fi lak′tik), adj. 

Collins Concise English Dictionary © HarperCollins Publishers::

tachyphylaxis / ˌtækɪfɪˈlæksɪs/ noun

1. very rapid development of tolerance or immunity to the effects of a drug

Etymology: New Latin, from tachy- + phylaxis on the model of prophylaxis. See prophylactic