Black’s Law Dictionary offers only verbs.
The U.S. Fish & Wildlife Service is a little more helpful, not defining the term, other than the verb forms. but giving examples and explanations.
The U.S. Fish and Wildlife Service and the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service (the Services), finalized the regulations governing Incidental Take Statements (ITSs) for endangered species.
An ITS is an estimate by the Services of the “take” of a threatened or endangered species that is likely to result from an action by a federal agency. “Take” means to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct. ITSs are produced by the Services as part of a biological opinion resulting from consultations with the federal agencies under section 7 of the Endangered Species Act.
Incidental take can take many forms, not all expressible as direct or immediate injury or death to individual animals. Some take can be in the form of a decrease in biological fitness due to reduced ability to breed or a shortened lifespan. Further, the Services have found that in many cases, the biology of a listed species or the nature of the proposed action can make it impractical to detect or monitor take of individual animals. In these cases, evaluating impacts to a “surrogate” (e.g., habitat, ecological conditions or similarly affected species) may be the most reasonable and meaningful way to describe the amount or extent of anticipated take of listed species.”