Would help if you gave context

But here are some

CAT
CAT is an abbreviation for Computer-Aided Tomography

Tomography
Tomography is the technique of using X-rays or ultrasound waves to procure
images of structures deep within the human body for diagnostic purposes. In
modern medical imaging there are several techniques, such as the CAT scan
(computerized axial tomography).

CAT computer-aided test


CATIS

CATIS is an abbreviation for Common Applications and Tools Integration
Services


CATV
CATV is an abbreviation for Common Antenna TeleVision; Community Antenna
TeleVision

CAT - Cathode

Cat Whisker -- A whisker like probe used in Crystal Radio

And of course CAT = Catalog as in Cat number



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CL -- I doubt, therefore I might be !