biosafety level bio·sa·fe·tylevel uncommon noun 1. the level of safety from exposure to infectious agents; depends on work practices and safety equipment and facilities Synonymsbiosafety level Related words Word family biosafety level 1biosafety level 2biosafety level 3biosafety level 4 Broader terms grade Narrower terms biosafety level 1biosafety level 2biosafety level 3biosafety level 4 WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.