“ . . entailed, in default of heirs male, on a distant relation . . .” (29)

Entailment is placing restrictions on an inheritance – in this case, restricting the inheritance of the manor to a male heir, thus making the Bennet daughters ineligible. Frequently in Austen’s time, estates that were entailed were to be handed down the male line, although it was possible to entail them to females. Because they have no brother to inherit the estate, it is likely that upon the death of their father they will be left poor and destitute when it exchanges hands. This entailment explains the fervor in the Bennet household around finding husbands for all five girls; the family wants to ensure that Jane, Elizabeth, Mary, Kitty, and Lydia will all be taken care of and able to live in the manner to which they are accustomed.

Source:

"Entailment - Definition and More from the Free Merriam-Webster Dictionary." Dictionary and Thesaurus -Merriam-Webster Online. Web. 13 Mar. 2010. http://www.merriamwebster.com/dictionary/entailment.