Definition of “valid”

adjective

1. having some foundation; based on truth
2. legally acceptable  ⇒ a valid licence 
3. 1. having legal force; effective
   2. having legal authority; binding
4. having some force or cogency  ⇒ a valid point in a debate 
5. logic (of an inference or argument) having premises and conclusion so related that whenever the former are true the latter must also be true, esp (formally valid) when the inference is justified by the form of the premises and conclusion alone. Thus (of an inference or argument) having premises and conclusion so related that whenever the former are true the latter must also be true, esp () when the inference is justified by the form of the premises and conclusion alone. Thus Tom is a bachelor; therefore Tom is unmarried  is valid but not formally so, while (of an inference or argument) having premises and conclusion so related that whenever the former are true the latter must also be true, esp () when the inference is justified by the form of the premises and conclusion alone. Thus is valid but not formally so, while today is hot and dry; therefore today is hot is formally valid Compare invalid² (sense 2)
6. archaic healthy or strong